Start by heating a little olive oil in a non-stick pan. As soon as it is heated, throw in the chopped mushrooms, onion and garlic. Saute for 5-6 minutes. Set aside.
Pour oat flour, water, grated cheese, salt, black pepper, olive oil into a bowl. Stir it up. Throw in the mushrooms, onion and garlic. Add the grated cheese.
Transfer to an oiled pan and bake in a preheated oven at 200C for 35'.
If you want, add some sesame seeds before baking.
Let your pie cool slightly before cutting.