Caroline's Stuffed Portobello Mushroom Burger
A tribute to Caroline, who declared this burger life-changing at my supper club. A meaty portobello is filled with a walnut–parsley mix for earthy depth, then tucked into toasted ciabatta with crisp fries and a bright tomato salad. Easy, indulgent, and entirely satisfying.
Photographed truthfully. If you cook it, yours will look like mine.
Ingredients
Other ingredients for the burger component
- 2 Portobello mushrooms | use Portobello; regular ol' flat mushrooms don't work well due to collapse!
- 10 ml olive oil
- 1 pinch salt | to season the mushroom
- 1 pinch ground black pepper | to season the mushroom
Ingredients for the burger filling
- 100 g red onion | unpeeled weight; small dice chop
- 10 ml rapeseed oil
- 1 pinch salt
- 1 clove fresh garlic | finely grated
- 30 ml balsamic vinegar
- 30 g walnuts | chopped into small pieces
- 10 g chia seeds
- 7 g ground flaxseeds
- 40 g hummus
- 10 g flat leaf parsley | neatly chopped into small pieces
- 30 g sun-dried tomatoes | neatly chopped into small pieces
- 2 pinches salt | to taste
- 2 pinches ground black pepper | to taste
Ingredients for the mustard mayonnaise
- 30 g vegan mayonnaise
- 8 g Dijon mustard
Ingredients for the salad dressing
- 1 tbsp balsamic vinegar
- 1 pinch salt | large
- 2 tbsp extra virgin olive oil
- ¼ tsp agave syrup | or maple syrup
- 1 pinch ground black pepper
To serve
- 125 g ciabatta buns | 2 units
- 10 g butter
- rocket | for underneath and on top of the burger
- gherkins | sliced, for the top of the burger
- french fries | maybe avoid big lumpy wedges of potato; thin crisp french fries are perfect!
- mixed leaves | for a mixed leaf, cherry tomato and gherkin side salad
- cherry tomatoes | for a mixed leaf, cherry tomato and gherkin side salad
- capers | for a mixed leaf, cherry tomato and gherkin side salad
Instructions
Prepare the burgers
- Preheat the oven to 180℃ fan (200℃ conventional).
- Put baking paper on a tray under the mushrooms.2 Portobello mushrooms
- Rub oil into the mushrooms and make sure you season the mushrooms.10 ml olive oil, 1 pinch salt, 1 pinch ground black pepper
- Peel and small-dice-chop the red onion. Cook on a low heat in some oil and a pinch of salt. Ensure these onions are super soft and translucent. Grate in the peeled garlic clove. Chop the stalk of the mushrooms into small pieces and add to the pan to reduce.100 g red onion, 10 ml rapeseed oil, 1 pinch salt, 1 clove fresh garlic
- When the onions are cooked, add the balsamic vinegar to deglaze the pan.30 ml balsamic vinegar
- Add the walnuts, chia seeds and ground flaxseed to the pan.30 g walnuts, 10 g chia seeds, 7 g ground flaxseeds
- Add the hummus to the pan and stir well to bind the ingredients.40 g hummus
- Chop up the sun-dried tomato ready for later.30 g sun-dried tomatoes
- Chop up the parsley and add to the pan.10 g flat leaf parsley
- Taste and season the mix. You want to have a good solid punchy flavour in this stuffing.2 pinches salt , 2 pinches ground black pepper
- Stuff the mushrooms with this mix and press firmly into the mushrooms.
- Add the sun-dried tomatoes to the top.
- Place into a pre-heated oven, 180 C fan for 25 minutes.When are the burgers cooked? They will have relaxed and oozed a little. They need to relax. If the burger is undercooked, the mushroom is chewy.
Prepare the burger bits
- Make the mustard mayonnaise by adding mustard to the mayonnaise.30 g vegan mayonnaise, 8 g Dijon mustard
- Slice some gherkins - please try adding the textural crunch and the acid of gherkin to this burger stack!gherkins
- Make the salad dressing: dissolve the salt in the vinegar, and then add the remaining ingredients.1 tbsp balsamic vinegar, 1 pinch salt, 2 tbsp extra virgin olive oil, ¼ tsp agave syrup, 1 pinch ground black pepper
- Chop a small handful of capers... Add the capers to the mixed salad leaves.capers
- Chop some cherry tomatoes for the salad, add a pinch of salt if you're going to eat soon; if not, don't salt yet!cherry tomatoes
Build your burger! Assemble in this order…
- Slice and toast your ciabatta. Spread butter to the burger top and bottom. Add tomato sauce to the burger bottom. Add rocket to the burger bottom and pull strands of rocket out so you can see it nicely.125 g ciabatta buns, 10 g butter
- Burger
- Gherkin slices
- Mayonnaise
- More rocket to decorate - pull out of the side of the burger so you can seerocket
- Burger bun top (buttered)
- Fries on the sidefrench fries
- Salad on the side - add some salad dressing just before serving - leaves don't like dressing being on too long! Don't forget to add the tomatoes…mixed leaves
Notes
- Multi-purpose: this filling could be used to fill pastry squares, which are folded over and sealed as pasties; the mustard mayo could be used on sandwiches to jazz things up!
- This meal has lots of elements. To avoid overwhelm, focus first on the burger. Just make the burger and get that right. Just make it for yourself to start with.
- About use of the oven: towards the end of preparing the burger filling, and assuming that you have a single oven, make sure there are two shelves available and heat it to the required temperature for your selected fries which might be up to 220 degrees C fan. You will cook your fries in the oven and during the last 20-30 minutes of cooking the fries, you will add your burgers to the same oven. Burgers need 180 degrees C fan for 25-30 minutes so if you are cooking your fries hotter than this, assume the burgers need less time.
Nutrition
Calories: 351kcalCarbohydrates: 28gProtein: 10gFat: 25gSaturated Fat: 3gPolyunsaturated Fat: 14gMonounsaturated Fat: 7gTrans Fat: 0.01gSodium: 149mgPotassium: 1106mgFiber: 9gSugar: 13gVitamin A: 565IUVitamin C: 17mgCalcium: 108mgIron: 4mg
Nutritional values are estimates only and will vary depending on specific ingredients used. Nutrition is per serving. Information is for the main recipe, not optional accompaniments.
Tried this recipe?Let us know how it was!
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© The Golden Polar Bear, 2025. Recipes and photography by Julia Savory. If you share this, please pass it along with kindness and if possible share a link back to this site. #ForTheAnimals