Combine all ingredients in a mixing bowl. Spray a small non-stick skillet with cooking spray. Preheat to medium. Pour egg mixture into skillet. As egg mixture sets at the edges, with spatula, gently lift cooked portion to allow uncooked egg to flow underneath. Cook until bottom is set and top is almost set. Slide frittata onto a plate, then invert back into skillet. Cook another 1 to 2 minutes to cook second side**. Serve on a warm plate.
** If you prefer, use an oven proof skillet and place under a preheated broiler for a few seconds to set frittata top.