01 - Set oven temperature to 375°F. Allow to preheat completely.
02 - Coat each cavity of a 12-cup muffin tin lightly with nonstick spray.
03 - Whisk together eggs, milk, salt, and pepper in a large bowl until fully blended.
04 - Fold chopped spinach, diced bell pepper, and shredded cheddar cheese into the egg mixture for even distribution.
05 - Pour mixture evenly into prepared muffin tin, filling each cup about three-quarters full.
06 - Transfer muffin tin to oven and bake for 18–22 minutes or until centers are set and edges are lightly golden.
07 - Allow muffins to cool in tin for 5 minutes, then carefully remove using a small offset spatula. Serve warm or at room temperature.