Heat a tablespoon of olive oil in a 10-inch cast iron skillet or non-stick pan. When hot, add the sausage and cook until lightly brown, about 6 minutes.
Add the peppers, onions and garlic and sauté for 3 minutes until the onions become translucent. Stir in the paprika, cumin and salt and cook for 1 minute more.
Add the tomatoes to the pan in an even layer, nestling them in the sausage/onion/pepper mixture. I like to artfully arrange them in a flower shape (because I like pretty things), but you do you.
Pour the egg whites into the pan and cook for 30 seconds before lowering the heat to low. You want the pan to be very hot when you add the egg whites so that the bottom sets, and then you want to cook your frittata slowly.
Cook your frittata for about 10 minutes, and then add the crumbled feta and cook for another 2-3 minutes. (Turn on your broiler while the frittata is cooking!) At this point, the sides of your frittata should be set, but the top should still be a little bit runny.
Carefully transfer your frittata to the broiler and cook for 3-4 minutes until it puffs up and the top gets lightly browned. Make sure to keep an eye on it, people! If you leave it under the broiler too long, the frittata will get grossly dry and tough. Remove the frittata from the broiler (using a dish towel or oven mitts, please) and let it rest for five minutes.
Sprinkle the top of your frittata with chopped parsley, slice and serve!