Heat three tablespoons of oil in a pan and sauté the onion until it is translucent. Add the courgette, carrots and pepper and cook over low heat until soft.
In the meantime make the bechamel. Put the butter in a saucepan and when it melts, add four tablespoons of flour and brown it slightly. Add a cup of milk and the pepper, and stir constantly over low heat until it thickens.
Put the eggs in a bowl with the remaining flour and milk. Whip well with whisks and in a pan heat the remaining oil to make four omelets (one at a time) with the egg mixture.
Put some of the vegetable filling in the middle of each omelet with two tablespoons of bechamel. Fold over, put in an oven tray and cover with the remaining bechamel and grated cheese.
Bake au gratin in the oven until the top layer is slightly brown and serve.