Had this at mom's and it was pretty good...
4 c shredded unpeeled zucchini
1/2 tsp salt
1/2 c grated Parmesan cheese
2 c shredded mozzarella cheese
1 c shredded cheddar cheese
1 lb ground beef
1/2 c chopped onion
1 can Italian tomato sauce
1 medium green pepper, chopped
Place zucchini in a strainer; sprinkle with salt. Let stand for 10 minutes; squeeze out moisture.
Combine zucchini with eggs, Parmesan, mozzarella, and cheddar cheeses. Press into greased 9X13 inch 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 or longer, until heated through.