Preheat the oven to 400 degrees F. Spray a medium skillet with cooking spray and saute your chopped onion for 3 to 4 minutes, until translucent. Add your spinach and saute until just wilted.

Place spinach-onion mixture in a small glass dish (or you can use a small skillet) and crack 3 egg whites over top. Season with a bit of salt and pepper, add sliced tomatoes and bake in oven for 17 minutes. Serve with fresh fruit and enjoy!