Meanwhile, in a large skillet, cook beef over medium heat until no longer pink; drain. Stir in taco seasoning.
In a small bowl, combine egg whites and ricotta cheese.
In each of two 13-in. x 9-in. x 2-in. baking dishes, layer four noodles, 3/4 cup ricotta mixture, half of the beef mixture and 1-1/3 cups cheddar cheese. Top each with four noodles, 3/4 cup ricotta mixture, 1-1/2 cups salsa and 1-1/3 cups cheese. Repeat.
Cover and freeze one casserole for up to 3 months.
Bake the second casserole, uncovered, at 350° for 35-40 minutes or until heated through. Let stand for 10 minutes before cutting.
Yield: 2 casseroles (8 servings each).
To use frozen casserole: Thaw in the refrigerator for 8 hours. Bake as directed.