Preheat the oven to 350°F (175°C). In a mixing bowl, combine the diced pineapple, brown sugar, cornstarch, and vanilla extract. Mix well and pour into a greased baking dish.

In another bowl, combine the rolled oats, flour, brown sugar, melted butter, and cinnamon. Mix until crumbly.

Sprinkle the oat topping evenly over the pineapple mixture in the baking dish. Bake in the preheated oven for 30 minutes or until the topping is golden brown.

Let cool for a few minutes before serving. Enjoy warm or at room temperature.