Preheat the oven to broil. Place the oven rack 4 inches from the heat source.
Use cooking spray to lightly coat a heavy, oven-proof skillet. Add the peppers and mushrooms to the skillet. Saut� over medium heat for about 5 minutes or until the vegetables are tender.
Whisk together the egg whites and 1/2 cup of the salsa in a small bowl. Add the egg white mixture to the vegetable mixture in the skillet, and cook for about 5 minutes or until partially set. While cooking, don't blend or scramble the mixture. Top with the cheddar cheese.
Place the skillet in the oven and cook for 5 minutes or until the eggs set completely and the cheese melts.
Cut the frittata into two portions and set on individual plates. Top each portion with 1 tablespoon salsa and serve immediately.
