Preheat oven to 350°F
Rinse and cut rhubarb into slices
In a 9-inch round baking dish, combine rhubarb, ½ cup sugar, and ¼ teaspoon cinnamon, and mix together
In a mixing bowl, combine flour, brown sugar, rolled oats, salt, and melted butter
Mix all crumble topping ingredients together until it forms a crumbly consistency
Spread the crumble mixture over the rhubarb until it reaches the sides of the baking dish
Bake at 350°F until golden and cooked through
