Wash the pork fillet, dab dry and cut into 16 thin medallions. Wash the cherry tomatoes, clean and trim the mushrooms. Cut both in half. Peel onion and cut into rings.
Wash the thyme and pluck the leaves from the stalks. Season medallions with salt and pepper. Heat the oil in a pan, fry the meat for about 2 minutes on each side, remove and keep warm. Sauté the onions in the frying fat, fry the mushrooms for about 2 minutes.
Add the tomato halves. Season with salt, pepper and thyme. Toast slices of bread, cut diagonally in half. Spread meat and vegetables on top and garnish with thyme.