Finely chop the leek and sauté in a pan with the butter.
Add the diced zucchini and sweet potato and stir.
Add salt, pepper, and desired herbs.
Cook over medium heat for about 15 minutes (it has to be soft) stirring the mixture making sure that it does not stick.
In a bowl beat half of the eggs, add half of the mixture from the frying pan and sprinkle in the cheese. Pour into a non-stick frying pan and make the omelet.
Repeat the previous step to make the second omelet.
Assemble the dish by placing the first tortilla on the plate, then spread the tomato sauce on top, along with the tuna and spinach, and then cover it with the other tortilla. Garnish with more tomato sauce and a few more spinach leaves. Voila!