Portobello Mushroom, Balsamic Onion and Goat’s Cheese Burgers

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.