01 - Preheat the oven to 350°F (180°C). Lightly grease a 12-cup muffin pan or line with silicone baking liners.
02 - In a skillet over medium heat, cook turkey sausage, breaking it apart with a spatula, until thoroughly browned. Drain any excess oil.
03 - Add diced red bell pepper and chopped spinach to the skillet. Sauté for 2 to 3 minutes until the vegetables have softened. Remove pan from heat and allow mixture to cool slightly.
04 - In a large mixing bowl, whisk together eggs, milk, garlic powder, paprika, salt, and pepper until well blended.
05 - Add cooked sausage mixture, sliced green onions, and shredded cheddar cheese (if using) to the egg mixture. Stir until evenly combined.
06 - Evenly portion the mixture into each muffin cup, filling each about three-quarters full.
07 - Bake for 20 to 25 minutes, or until the egg muffins are set and lightly golden on top.
08 - Let the muffins rest for 5 minutes in the tin before transferring to a rack. Serve warm or cool completely for storage.