Preheat your oven to 375°F (190°C).
Lightly grease a 12-cup muffin pan with cooking spray or oil.
In a large bowl, whisk the eggs and cottage cheese until well combined.
Stir in the cheddar cheese, red bell pepper, spinach, green onion, salt, and black pepper.
Divide the mixture evenly among the 12 muffin cups, filling each about two-thirds full.
Bake for 18–22 minutes, or until the egg muffins are set in the center.
Let them cool for a few minutes before carefully removing them from the pan.
Serve warm or allow them to cool completely before storing.