Clean, wash and finely dice the zucchini. Peel and finely dice the onion and garlic. Wash basil, dab dry and chop. Drain the mozzarella and cut into small cubes.
Heat 2 tablespoons of oil. Fry the onion, garlic and zucchini for 3-4 minutes. Take them out. Whisk eggs, season with salt and pepper. Fold in basil. Heat 2 tablespoons of oil in a pan (22 cm Ø).
Add the egg mixture. Spread the zucchini and onion mixture and mozzarella on top. Leave to set at medium heat for 6-8 minutes. Slide the omelette onto a plate and put it back into the pan upside down.
Fry for another 3 minutes. Cut the frittata into 8 cake pieces. Cover each with 1 slice of ham, garnish with basil and serve.