Preheat your oven to 350°F (175°C). Generously spray a 12-cup muffin tin with non-stick cooking spray. To ensure the eggs don’t stick, you can also use silicone muffin liners, which make removal very easy.
In a large mixing bowl, crack the 8 eggs and add the 1 cup of liquid egg whites. Add the salt, black pepper, and garlic powder. Whisk vigorously until the mixture is smooth and the yolks are fully combined with the whites.
Finely chop the spinach, red bell pepper, and onion. If you are using turkey sausage, ensure it is already cooked and crumbled. Keeping the pieces small helps the muffins hold their shape better.
Divide the chopped spinach, diced peppers, onions, turkey sausage, and shredded cheese evenly among the 12 muffin cups. This ensures that every bite has a perfect balance of toppings.
Carefully pour the egg mixture into each muffin cup, filling them about 3/4 of the way to the top. Do not overfill, as the eggs will rise slightly while baking.
Place the muffin tin in the center rack of the oven. Bake for 20 to 25 minutes, or until the centers are set and the tops are lightly golden. Let them cool in the pan for 5 minutes before using a plastic knife or spatula to gently pop them out.