Preheat oven to 375°. Coat an 11-inch x 7-inch or 9-inch square baking dish with cooking spray.
In large nonstick skillet over medium-high heat, heat 2 teaspoons of the oil. Add the potatoes and cook, stirring occasionally, until lightly browned and cooked through, about 10 to 12 minutes. Turn into a large bowl.
Return the skillet to the heat and add the remaining oil. Stir in onion, bell pepper and sausage. Cook, stirring occasionally, until sausage is browned, about 5 to 6 minutes. Add to the bowl with the potatoes and mix well. Turn into prepared baking dish.
In medium bowl, whisk together the egg whites, eggs, milk, salt and pepper. Pour egg mixture evenly over the potato mixture. Sprinkle top with cheese. Bake until eggs are set and cheese has melted, about 25 to 28 minutes.
Nutritional Analysis per serving: 220 calories, 17 g protein, 16 g carbohydrates, 9 g fat, 3 g saturated fat (39% of calories from fat), 132 mg cholesterol, 1 g fiber, 436 mg sodium.