Preheat oven to 350 degrees F. Coat 18 muffin cups with cooking spray. In a large bowl, combine cake mix, oil, pineapple, eggs, and cinnamon. Add enough water to reserved pineapple juice to make 1/2 cup; add it to bowl then beat with an electric mixer until mixture is thoroughly combined.
Stir in banana, 1/2 cup walnuts, and 1/4 cup cherries; mix well then pour into prepared muffin cups. Sprinkle with remaining nuts and cherries. Bake 22 to 25 minutes, or until a toothpick inserted in center comes out clean. Let cool 10 to 15 minutes, then remove from muffin cups. Let cool completely.