Preheat oven to 350 degrees F (175 degrees C). Mix meatloaf meat, apples, onion, stuffing mix, celery, milk, water, eggs, garlic powder, salt, and black pepper together in a bowl until ingredients are evenly combined. Spread cream of mushroom soup into a 9x5-inch loaf pan. Spoon meat mixture into the loaf pan and use a spatula to gently flatten the top of the loaf. Bake in the preheated oven until no longer pink in the center, about 1 1/2 hours. An instant-read thermometer inserted into the center should read at least 160 degrees F (70 degrees C). Cool in pan for 5 to 10 minutes. Flip meatloaf pan upside-down onto a serving platter so the cream of mushroom soup is on the top of the loaf.