Preheat oven to 350°F. Spray a standard muffin pan with cooking spray.
Heat oil in large skillet over medium-high heat. Add pepper and onion. Cook and stir for 5 minutes.
Whisk eggs, egg whites, salt mustard and dill. Stir in cooked pepper and onion, dill and cheese.
Portion 1/4 cup into each muffin cup. Bake for 20 to 25 minutes or until set.