Mix flour, zucchini, sugar, cheese, baking soda, powder and salt together; set aside. Melt butter; stir into buttermilk. Beat eggs in medium bowl; add butter/buttermilk and onion; stir into flour mixture. (Batter will be thick.) Spread in greased and floured 9x5x3 inch loaf pan. Bake at 350 for 1 hour. (Use toothpick inserted at center to test for doneness.