Preheat the oven to 350 degrees F. Lightly grease 12 muffin cups or line with paper muffin liners.

Heat a large skillet over medium-high heat. Stir in sausage and cook until crumbly, evenly browned, and no longer pink, 10 to 15 minutes. Drain off grease.

Beat eggs in a large bowl. Stir in onion, green pepper, salt, pepper, and garlic powder. Mix in sausage and Cheddar cheese. Spoon into the prepared muffin cups.

Bake in the preheated oven until a knife inserted near the center comes out clean, 20 to 25 minutes.