Combine casserole ingredients: Preheat oven to 350°F. In a medium size bowl, combine sugar, flour, and reserved pineapple juice. Add pineapple chunks and toss well to combine. Spoon pineapple mixture into 8x8-inch casserole dish, and top with shredded cheese.
Add cracker topping: Combine crushed Ritz crackers and melted butter. Spread Ritz cracker topping evenly on top of pineapple mixture.
Bake casserole: Bake at 350°F for 30 minutes, or until bubbly.
