Preheat and prep: Heat your oven to 350°F (175°C).
Lightly coat a 12-cup muffin tin with nonstick spray. This helps the muffins release cleanly and avoids sticking.
Cook the sausage: Warm a skillet over medium heat. Add the turkey sausage and cook, breaking it up with a spatula, until browned and fully cooked, about 5–7 minutes.
Transfer to a plate lined with paper towels to drain excess fat.
Sauté the veggies: In the same skillet, add olive oil, then the onion and bell pepper. Cook until softened and slightly golden, about 4–5 minutes. Stir in the chopped spinach and cook 1 minute more, until wilted.
Remove from heat.
Mix the egg base: In a large bowl, whisk the egg whites with salt, pepper, garlic powder, and smoked paprika. Fold in the parsley.
Assemble: Divide the cooked sausage and vegetables evenly among the muffin cups. If using cheese, sprinkle a small amount into each cup.
Add egg whites: Pour the egg white mixture into each cup, filling about 3/4 full.
Stir gently with a spoon in each cup to distribute fillings.
Bake: Place the tin on the middle rack and bake for 18–22 minutes, until the muffins are set and the tops look just dry. A toothpick should come out mostly clean.
Rest and release: Let the muffins cool in the tin for 5 minutes. Run a thin knife around the edges to loosen, then lift them out to a rack to finish cooling.
Serve: Enjoy warm with hot sauce, salsa, or a dollop of Greek yogurt.
They’re great with fruit, toast, or avocado on the side.