Put some salt on the grated courgettes and let them in a colander to get the excess water out. Squeeze them also with your hands.
Saute in a saucepan, using the olive oil, the onions and the courgettes. Remove from the heat and add the mint, the eggs, 2/3 of the cheese, salt, pepper and the flour. Stir the mixture.
Grease a baking dish, sprinkle bread crumbs on it and pour the mixture in. Scatter the remaining cheese and bake in preheated oven for 45'-45'. Allow to cool before serving.