01 - Preheat oven to 375°F. Lightly grease a 12-cup muffin tin with olive oil or nonstick cooking spray.
02 - Heat olive oil in a skillet over medium heat. Add red onion and bell pepper; cook 3–4 minutes until softened. Stir in spinach and cook 1 minute until wilted. Remove from heat and cool slightly.
03 - In a large bowl, whisk together eggs, milk, salt, pepper, and Italian herbs until fully combined.
04 - Fold in cheddar cheese, Parmesan, sautéed vegetables, and cherry tomatoes until evenly distributed.
05 - Divide the egg mixture evenly among the prepared muffin cups, filling each about 3/4 full.
06 - Bake for 18–20 minutes, or until the muffins are puffed and set in the center.
07 - Let cool in the tin for 5 minutes before removing. Serve warm or at room temperature.