Peel and finely chop the onion. Wash the thyme, dab dry, put something aside for garnishing. Chop the rest finely. Knead minced onion, thyme, egg and breadcrumbs. Season with salt and pepper.
Put the mince in a quiche tin (28 cm Ø) and press it to a smooth base. Drain the corn. Wash, clean and slice the tomatoes. Cut mozzarella into slices. Spread the corn and tomatoes on the chopped mass, place the cheese on top.
Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 20-25 minutes. Serve quiche garnished with thyme.