Step 1 - Preheat the oven to medium-high temperature (190°C).
Step 2 - In a bowl, mix the 1 cup of sugar, 3 tablespoons of flour, calafates and rhubarb. Place the mixture in a baking dish. Set aside.
Step 3 - In another bowl, mix flour, brown sugar, butter and oatmeal with your fingers until crumbs are formed. Distribute the crumbs over the fruit in the reserved bowl.
Step 4 - Bake 30 minutes in the preheated oven or until lightly browned. Serve warm with vanilla ice cream.