8 large Portobello mushrooms, stems removed
2 large red onions, thinly sliced
1 clove garlic, crushed
2 teaspoons balsamic vinegar
400 grams spinach leaves, washed
sea salt and ground pepper
4 burger buns, toasted and buttered (I used brioche buns)
mayonnaise, for spreading
100 grams soft goat’s cheese
Heat a sauté pan or barbecue until hot. Brush the mushrooms with oil and season both sides. Cook until tender then set aside, covered to keep warm.
Add a little oil to the sauté pan and cook the onion and garlic with a good pinch of salt until soft. Add the balsamic vinegar and cook for 1 minute then transfer the onions to a plate.
Add the damp spinach leaves to the same hot pan and cook, turning with tongs, until just wilted.
To assemble: Spread the buns with mayonnaise and top with a pile of spinach, then the mushrooms. Crumble over the goat’s cheese and add a stack of balsamic onions. Replace the tops and serve immediately.