You know a recipe qualifies as simple when you can throw this together while still dressed in work clothes after a long day in the office.
My husband and I were both tired. We had dinner but nothing that I could bring for lunch. So I quickly sautéd a sliced yellow onion and sliced red bell peppers in a skillet (yellow onions first, let it sweat a bit, then add bell peppers, using extra virgin olive oil of course, salt and fajita seasoning to taste). In the meantime, I cracked 4 eggs, added Cotija cheese and fresh black pepper, and whipped it until everything was mixed well. When the onions and bell peppers were cooked, I added in the mixture and let it sit for a few minutes (until the bottom should be cooked). While the top was still a bit runny, I put it in the oven on Broil to cook the top.
That was it! In about 30 minutes, I was done and had two slices of frittata for lunch (heated for 45 seconds in the microwave).