* Pour 2 tablespoons olive oil in a non-stick skillet on medium heat. Lightly beat the eggs in a bowl, until fully combined. Add salt and pepper.
* Add the diced mozzarella and the grated parmigiano cheese.
* When the oil is hot, pour the egg mixture in the skillet.
* When the egg starts to solidify, using a fork lightly scramble the center to let all the egg penetrate on the bottom. Shake lightly the pan back and forth to loosen the frittata and use a fork to loosen it from the edges of the pan. Lift the frittata to check that the bottom is cooked and golden.
* Make sure the egg on the top is not too running, then place on the pan a dish slightly larger than the pan.
* Rotate the pan and the dish together so that now the frittata is upside down on the dish.
* Add 2 tablespoons of olive oil to the skillet then slide the frittata back into the pan so that the uncooked face is now on the pan. Lift the frittata to check that the bottom is golden.
* Slide the frittata on a serving dish and serve hot at once.