Grate the Parmesan cheese on a coarse grater. Cut the sausage into cubes.
Cut the bell pepper into small cubes and also finely chop the onion.
Add vegetable oil to a heated frying pan. Fry the bell pepper on low heat, stirring, for 5 minutes.
Break the eggs into a deep bowl. Add milk and salt to taste and beat the ingredients well with a fork or whisk.
Place the chopped vegetables and sausage in a baking dish. Pour the egg and milk mixture over the filling and sprinkle everything with grated cheese.
Place the pan with the omelette mixture in the oven and bake the omelette for 25 minutes until it is completely baked. You can check the readiness of the omelette with a toothpick.
Serve the omelette garnished with your favorite herbs. Enjoy!