Place zucchini in strainer; sprinkle with salt. Let stand for 10 minutes. Squeeze out moisture.
Combine zucchini with the eggs, Parmesan and half of the mozzarella and cheddar cheeses. Press into greased 13-in. x 9-in. baking dish.
Bake, uncovered, at 400° for 20 minutes. Meanwhile, cook beef and onion over medium heat until meat is no longer pink; drain. Add tomato sauce; spoon over zucchini mixture.
Sprinkle with remaining cheeses; add green pepper. Bake 20 minutes longer or until heated through.