Mix lemon juice and milk; set aside. Preheat oven to 350. Grease 9X5 loaf pan. Combine flour, zucchini, sugar, cheese, baking powder, soda and salt. In saucepan, melt butter; stir in milk and lemon juice, eggs, and onion until smooth. Add liquid mixture to dry mixture just until mixed. Spread in prepared pan. Bake 55-60 min until toothpick comes out clean and loaf pulls away from sides of pan.