Coat a medium nonstick skillet with cooking spray. Heat skillet over medium heat; add bell pepper, cumin, and, if desired, crushed red pepper. Cook and stir until tender, about 3 minutes. Add egg; cook, without stirring, until mixture begins to set on the bottom and around edge. With a spatula or large spoon, lift and fold the partially cooked egg mixture so that the uncooked portion flows underneath. Continue cooking for 2 to 3 minutes or until the egg mixture is cooked through but is still glossy and moist.