Set a large nonstick skillet over medium-high heat. Lightly coat with cooking spray. Add the breakfast sausage and cook, stirring occasionally, until the sausage is browned and just cooked through.
Spread the cooked sausage and green chiles evenly over the bottom of the prepared baking dish.
In a large bowl, whisk together the eggs, egg whites, water, salt and pepper. Pour the egg mixture over the sausages. Sprinkle the cheese over top.
Baked until the casserole is set and a knife inserted in the center comes out clean, about 20 minutes.