Preheat oven to 400°. Place zucchini in colander; sprinkle with salt. Let stand 10 minutes, then squeeze out moisture. , Combine zucchini with eggs, Parmesan and half the mozzarella and cheddar cheeses. Press into a greased 13x9-in. or 3-qt. baking dish. Bake 20 minutes. , Meanwhile, in a large saucepan, cook beef and onion over medium heat until meat is no longer pink, breaking meat into crumbles; drain. Add tomato sauce; spoon over zucchini mixture. Sprinkle with remaining cheeses; add green pepper. Bake until heated through, about 20 minutes longer., Freeze option: Cool baked casserole; cover and freeze. To use, partially thaw in refrigerator overnight. Remove from refrigerator 30 minutes before baking. Preheat oven to 350°. Unwrap casserole; reheat on a lower oven rack until heated through and a thermometer inserted in center reads 165°.