Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Line a baking tray with baking paper. Knead minced meat, breadcrumbs, egg, approx. 1 teaspoon salt and 1⁄2 teaspoon pepper. Form 2 flat cakes (approx. 18 cm Ø) and place them on the baking tray.
Bake in a hot oven for about 15 minutes.
Peel garlic and dice finely. Clean the mushrooms, halve them and fry them in hot oil. Season with salt and pepper, take out. Sauté garlic in frying fat. Add tomatoes and 1 teaspoon oregano, bring to the boil and simmer open for about 5 minutes.
Season to taste with salt and pepper. Remove the pizzas. Spread sauce, mushrooms and cheese on top. Bake at the same temperature for 10-15 minutes.