Preheat your oven to 350°F (175°C) and prepare an 8-inch square pan by lining it with foil and spraying it lightly with cooking spray.

Melt 1/2 cup of unsalted butter in a large microwave-safe bowl. Stir in the flour, oats, granulated sugar, brown sugar, and salt until well combined, setting aside a heaping cup for later.

Press the remaining mixture into the bottom of the prepared pan to form the crust.

In a separate bowl, combine mango, sugar, lemon juice, and corn starch. Stir gently until the mango is coated and slightly thickened.

Spread the mango mixture over the crust and sprinkle the reserved crumb mixture on top.

Bake for about 50 minutes until edges are set and center looks firm.

Allow to cool in the pan for an hour before lifting out and slicing into squares.