In a pan, saute onion potato, bell pepper, tuna flakes, and mushroom (salt is optional). Cook for 5 minutes then set aside.
In a heated non-stick pan, add a little oil then pour the beaten egg. When egg is almost done, add the cooked ingredients on the half side of the egg.
Flip the egg to form an omelet. Turn the omelet. Serve hot.
This has carbohydrate and protein so it can be a meal itself. Delicious and easy to cook.