Brown ground meat with onion and garlic. Add rice, water, and sauce. Reduce heat, cover, and simmer for 20 minutes, or until rice is done.
Meanwhile, shred cheese. Wash and split peppers or zucchini. Split the peppers into thirds or quarters, depending on size. Or split zucchini in half. Remove seeds from peppers or scoop out the seeded center of zucchini, leaving about 1/2 inch all around. Arrange peppers or zucchini in a 9"x13" or 10"x15" pan, hollow side up.
When the meat-rice mixture is cooked, turn off heat. Add 1 1/2 cups cheese and stir until melted. Stuff the peppers or zucchini. Top with remaining 1 cup cheese and 1 1/2 cups spaghetti sauce. Bake uncovered at 350F for 30 minutes for peppers, or 45 minutes for zucchini, until heated through and sauce is bubbly.