01 - Preheat oven to 350°F. Lightly grease a 6-cup muffin tin with olive oil or nonstick spray.
02 - In a large mixing bowl, whisk eggs, milk, salt, black pepper, and paprika until fully blended.
03 - Fold in red bell pepper, baby spinach, spring onion, and shredded cheddar until distributed evenly.
04 - Divide the mixture evenly among muffin cups, filling each about three-quarters full.
05 - Transfer to oven and bake for 18–22 minutes, or until the muffins are puffed and the centers are just set.
06 - Remove pan from oven and let muffins cool for 5 minutes. Run a knife around edges to release. Serve warm or cool completely for storage.