Preheat the oven to 350 degrees F. Grease 8 muffin tin cups with cooking spray. Make sure you spray the cups well. Set aside.
In a medium bowl, whisk together egg whites and eggs. Whisk in skim milk and season with salt and pepper, to taste. Stir in the green onion, kale, and roasted red peppers.
Pour egg mixture evenly into the muffin cups. Distribute cheese equally between each muffin cup.
Bake egg muffins for 20 minutes, or until the muffins are firm in the center. Remove from oven and gently go round each egg with a butter knife. Serve warm.
Note-you can store the egg muffins in the fridge for 3-4 days and reheat them in the microwave. They also freeze well!