Lightly oil a 12-cup mini muffin tin or 6-cup tin for regular size muffins.
In a mixing bowl, whisk together eggs, bell pepper, zucchini, onion, cheese, and salt and pepper, until light and fluffy.
Pour batter into muffin cups, filling each tin about 3/4 full. Sprinkle an even amount of cheese onto each muffin. Bake for 15-20 minutes or until the eggs are set. Enjoy!