1.Heat the oven to 400°F.
2.Spray a 9-inch pie plate with cooking spray. Heat the oil in a 10-inch nonstick skillet over medium heat.
3.Add the onion and cook for 2 minutes, stirring occasionally.
4.Add the asparagus and bell pepper to the onion and cook for 3 to 4 minutes or until slightly tender, stirring occasionally.
5.Pour the vegetables into the pie plate.
6.Combine the egg substitute, sour cream and black pepper in a medium bowl; whisk until blended.
7.Pour the egg mixture over the vegetables.
8.Bake the frittata for 15 to 20 minutes or until set, sprinkling with the Cheddar cheese during the last 5 minutes of baking.
9.Let the frittata stand for 5 minutes before slicing and serving.