Heat 2 tablespoons of olive oil in a large frying pan over medium heat. Add the onions and cook for 4 minutes or until the onions are transparent. Add the sweet and hot pepper, and the tomatoes; cook for 2 to 3 minutes and let cool in the pan.
Crack the eggs into a bowl and beat in the cheese and salt. Add the cooled sautéed onions to the egg mixture and stir well. Wipe out the frying pan with a paper towel and add 1 teaspoon of olive oil to the pan. Heat the oil and then pour the egg mixture into the pan. Cover and cook for 5 or 6 minutes. When the liquid is set and the frittata moves easily in the pan, put a large plate over the pan and flip the frittata out onto the plate. Add another teaspoon of olive oil to the pan and carefully slip the frittata back in to cook the other side. Cover and cook for another 4 to 5 minutes.
If cooking in the oven, preheat to 325, dont cover and just place in oven for approx 20 min or desired doneness. I put extra parmesan over the top for the last 5 minutes.
Slide the frittata onto a serving platter; slice into wedges and serve immediately.