In a medium bowl, whisk together the egg whites, salt, and pepper.
In a large oven-safe skillet, heat the olive oil over medium-high heat. Add the onion, bell pepper, mushrooms, and bacon. Saute for 3 minutes, until the vegetables are just beginning to soften.
Reduce heat to medium-low and add the egg whites to the skillet. Stir to combine. Cook for 2 minutes, stirring occasionally.
Sprinkle the cheese over the top of the frittata and transfer the skillet to the preheated oven. Bake for 10-15 minutes, until the egg whites are set and the cheese is melted.
Remove from oven and let stand for 5 minutes. Sprinkle with parsley, if desired. Cut into wedges and serve.
Interesting Facts
Egg whites are a great source of protein and contain no cholesterol.
This frittata is a great way to use up leftover vegetables and bacon.
You can add any vegetables you like to this frittata, such as zucchini, spinach, or tomatoes.