Preheat the oven: Set to 350°F (175°C). Grease a 12-cup muffin tin with nonstick spray or use silicone liners.

Cook the sausage: In a skillet over medium heat, cook and crumble the turkey sausage until browned and cooked through. Drain excess fat if needed.

Sauté the veggies: Add 1 teaspoon oil to the same pan. Sauté onion and bell pepper for 3–4 minutes until slightly softened. Stir in garlic for 30 seconds. Add spinach and cook until just wilted. Remove from heat to cool slightly.

Whisk the base: In a large bowl, whisk egg whites with milk, salt, pepper, and smoked paprika. Stir in parsley or chives.

Combine the mix-ins: Fold in the cooked sausage, sautéed veggies, and cheese (if using).

Fill the muffin tin: Divide the mixture evenly among the 12 cups, filling almost to the top. Stir the bowl often so the sausage and veggies don’t settle.

Bake: Bake for 18–22 minutes, until the tops are set and just starting to turn golden around the edges. The centers should spring back lightly to the touch.

Cool and release: Let the muffins cool in the pan for 5 minutes. Run a thin knife around the edges if needed, then transfer to a rack to cool fully.

Serve: Enjoy warm, or let them cool before storing for meal prep.