Sauté mushrooms, leek and onions with a bit of olive oil in a frying pan, until soft. Season with salt and pepper and remove the pan from the heat.
Preheat oven to 220 degrees.
Spread tomato sauce on the pizza base.
Evenly distribute a layer of grated cheese.
Add sautéed vegetables.
Top off with the remainder of the cheese.
Bake in the oven for about 7-10 minutes until the cheese melts.