Preheat oven to 375°F.
In a 10-inch cast iron skillet, add mango, sugar, butter, flour, cornstarch, vanilla and salt.
Cook on stovetop over medium heat, stirring regularly, until bubbly and thickened.
Meanwhile, in a stand mixer with paddle attachment, add 1 cup flour, oats, sugar, cardamom and salt. Add the butter and mix until mixture holds together in coarse clumps, adding a splash of water, if needed.
When fruit is ready, drop large tablespoons of dough on top of warm fruit. Place into preheated oven and bake for 35-40 minutes, until the edges are bubbling and the top is golden brown.
Serve warm as is or topped with ice cream.