01 - Set oven to 350°F. Lightly grease a standard 12-cup muffin tin or line with silicone muffin liners.
02 - In a skillet over medium heat, cook turkey sausage, breaking up with a spatula, until evenly browned and fully cooked. Drain excess fat.
03 - Add diced red bell pepper and chopped spinach to the skillet. Sauté for 2 to 3 minutes, or until just softened. Remove from heat and set aside to cool slightly.
04 - In a large mixing bowl, whisk together eggs, milk, garlic powder, paprika, salt, and pepper until well combined.
05 - Add cooled sausage mixture, sliced green onions, and shredded cheddar cheese (if using) to the eggs. Stir until incorporated.
06 - Evenly spoon the mixture into prepared muffin cups, filling each about three-quarters of the way.
07 - Bake 20 to 25 minutes, or until muffins are set and lightly golden on top.
08 - Let muffins cool in the tin for 5 minutes. Remove and serve warm, or let cool completely for storage.