Heat the oven to 180 C (375F).

Grease a casserole dish with 1 tablespoon of olive oil

In a frying pan, over medium heat, add 1 tablespoon of the remaining oil, the chopped mushrooms, onion powder and garlic. Fry, stirring from time to time, until the mushrooms are browned.

Transfer the cooked mushrooms to a bowl to cool.

In a separate bowl, add eggs, milk, salt and pepper. Mix with a whisk, until it becomes a homogeneous composition.

Now place the grated boiled potatoes in the casserole, in layers, then put the cooked mushrooms in one layer, cover with the cheese layer and then pour the egg mixture over it.

Put it in the oven and let it cook for 35-40 minutes, or until the top layer turns golden.