Preheat oven to 375°F (190°C).
In a small ramekin or oven-safe dish, add fruit and sprinkle with granulated sugar.
In a bowl, mix oats, flour, brown sugar, and cinnamon. Cut in butter using a fork or your fingers until the mixture resembles coarse crumbs.
Sprinkle the crumble topping evenly over the fruit.
Bake for 20–25 minutes, or until the topping is golden and the fruit is bubbling.
Cool slightly and serve warm, topped with ice cream or whipped cream.