Preheat the oven to 350 degrees F (175 degrees C). Coat 2 loaf pans with cooking spray. Mix baking mix, zucchini, Cheddar cheese, sugar, and salt together in a large mixing bowl. Combine milk, eggs, and butter in a food processor and blend. Pour milk mixture into the bowl with the zucchini mixture. Mix together, folding with a spatula, until dry ingredients are blended in. Divide batter evenly between the prepared loaf pans. Bake in the preheated oven until golden brown, about 1 hour and 15 minutes. Cool pans on a wire rack for 10 minutes before inverting loaves.