Preheat oven to 350°F. Generously spray a non-stick or silicone muffin tin with nonstick cooking spray.
Heat olive oil into a a non-stick frying pan over medium-high heat. Add the bell pepper and onion and saute for 2 to 3 minutes. Stir in the meat, spinach and tomatoes and cook an additional 2 minutes. Place 1 heaping Tablespoon into each muffin cup.
Next whisk the egg whites into a medium-sized bowl. Stir in the salt and pepper. Then pour over the meat mixture in the muffin tin, leaving 1/4″ from the top.
Cook for 23 to 30 minutes, or until the egg has puffed and comes clean with a toothpick. Run a knife around the edges to pop the egg muffins out. Enjoy while hot. Add some extra tomatoes, a little salsa or hot sauce for a kick if desired.
Store in an airtight container in the refrigerator. Eat within 5 days.
Tip: Use an egg white carton to make this recipe even easier.If you'd like to add cheese, feel free to mix in 1/4-1/2 cup shredded cheddar or feta cheese before baking. Freezer tip: Allow egg muffins to completely cool and then place in an airtight container or ziptop bag. Then freeze for up to 3 months. Reheat in microwave for 45 seconds, or until warm.