Preheat oven to 350°F. Coat 4 cups of a muffin pan with olive oil spray.
In a bowl, whisk to combine egg whites and black pepper.
Divide mushrooms, broccoli, and bell pepper evenly between the 4 prepared muffin cups. Pour egg white mixture over vegetables, then top each with an equal amount of cheese and 1 sun-dried tomato half.
Bake for 20 minutes, or until eggs are set. Serve warm.
Notes
Makes 4 muffins. These can be refrigerated for up to three days, allowing you to prepare your breakfasts in advance.