Wash and slice the tomatoes. Peel and halve onions and cut them into strips. Wash lettuce leaves and shake dry. Clean the Portobello, removing the stalk. Heat butter in a large pan.
Fry the Portobello for 2-3 minutes on each side, flattening it with a spatula. Cut the cheese into slices. Place on the mushrooms, cover with a pan lid and melt the cheese.
Wash the shrimps and pat them dry. Heat the oil in a second pan. Fry the shrimps for about 3 minutes, turning them until they are nice and pink on all sides. Halve the lime and squeeze the juice of one half over the shrimps.
Season with a little salt.
Mix mayonnaise, remaining lime juice and chili. Season with salt and pepper. Roast the burger buns in a hot oven or on a toaster according to the instructions on the package. Slice the roll crosswise, spread both halves with the lime-chili-mayo.
Place 1 lettuce leaf, 1 cheese portobello, a few shrimps, tomato slices and onion strips on the bottom of each roll. Cover with the top half of the roll. Enjoy! Serve with roast potatoes or potato wedges.