01 - Preheat oven to 350°F (180°C). Lightly grease a 12-cup muffin tin or line with silicone liners.
02 - In a skillet over medium heat, cook turkey sausage, breaking it up with a spatula, until browned and cooked through. Drain off excess fat.
03 - Add red bell pepper and spinach to the skillet. Sauté for 2 to 3 minutes until the vegetables are softened. Remove skillet from heat and allow mixture to cool slightly.
04 - In a large mixing bowl, whisk together eggs, milk, garlic powder, paprika, salt, and black pepper until combined.
05 - Add cooked sausage mixture, green onions, and shredded cheddar cheese (if using) to the eggs. Stir until well incorporated.
06 - Evenly divide the mixture among muffin cups, filling each approximately three-quarters full.
07 - Bake for 20 to 25 minutes, or until the egg muffins are set and lightly golden on top.
08 - Allow muffins to cool in the tin for 5 minutes before removing. Serve warm, or cool completely for storage.