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 apart with a spatula, until evenly browned and fully cooked. Drain any excess fat.
03 - Add red bell pepper and chopped spinach to the skillet. Sauté for 2 to 3 minutes, until vegetables are softened. Remove skillet from heat and allow the mixture to cool slightly.
04 - In a large mixing bowl, whisk together the eggs, milk, garlic powder, paprika, salt, and pepper until smooth.
05 - Fold the sausage and vegetable mixture, green onions, and shredded cheese (if using) into the egg mixture until combined.
06 - Divide the mixture evenly among the prepared muffin cups, filling each about three-quarters full.
07 - Bake in the preheated oven for 20 to 25 minutes or until muffins are set and lightly golden on top.
08 - Allow muffins to cool in the tin for 5 minutes before transferring to a wire rack. Serve warm, or cool completely for storage.