Peel and chop the onion. Leave bacon in a pan until crispy, add onion and steam briefly. Remove from the pan, put bacon fat aside. Let the bacon mixture cool down.
Wash, clean and seed the tomatoes and dice the pulp. Dice the cheese as well. Wash the thyme, dab dry and remove the leaves from the stalks. Clean and trim the mushrooms. Remove the stalks and dice finely.
Mix mushroom stalks, tomatoes, thyme, cheese and bacon mixture, season with pepper. Sprinkle mushrooms with salt. Fill in prepared mixture. Put the mushrooms in a large ovenproof dish. Cut bread slices in half and cut into strips.
Spread around the mushrooms. Peel half of the garlic and dice coarsely. Spread the garlic cloves and diced garlic on the bread. Drizzle with oil. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 12-18 minutes.
In the meantime, wash and clean the salad and pluck into bite-sized pieces. Distribute on 4 plates. Mix bacon fat with vinegar and season with salt and pepper. Dribble over the salad. Take the mushrooms out of the oven and arrange on the plates.