In large non-stick skillet, brown beef over medium-high heat for 5 minutes. Add 1/2 cup salsa,and continue cooking for 2 minutes. In large bowl,whisk egg whites and milk. Season with salt & pepper. Coat large nonstick skillet with cooking spray and heat over medium-high. Add egg white mixture,and cook until nearly set(2-4 minutes).
Using a spatula to pull in sides and allow uncooked egg to run underneath. For extra fluffiness,cover the eggs for last 30 seconds. Sprinkle beef mixture,remaining salsa,and feta cheese on top of the omelet. Fold omelet and carefully slide onto serving plate.