Preheat oven to 350 F. Lightly spray two 6-cup muffin pans with olive oil cooking spray. Spray a nonstick skillet with cooking spray and briefly cook vegetables until tender. Place a small amount of vegetables in each of the muffin cups then fill the cups 3/4 full with egg whites. Sprinkle pepper and a small amount of cheese on top. Bake in oven for 10 minutes until they are just set. Cool in the pans. Note: I had mine in for closer to 20 minutes and didn't put the cheese on top until they were almost cooked.