Preheat your oven to 350°F (175°C) and line an 8-inch square baking pan with foil, greasing it lightly.

Melt ½ cup of unsalted butter in a microwave-safe bowl, then mix with flour, oats, sugars, and salt until sandy texture is formed. Reserve 1 cup for topping.

Press the remaining crumb mixture into an even layer at the bottom of the pan to create the crust.

In a bowl, combine chopped strawberries, granulated sugar, lemon juice, and cornstarch. Toss gently and let sit for about 5 minutes.

Spread the strawberry mixture evenly over the crust, then sprinkle with the reserved crumble topping.

Bake for approximately 50 minutes until golden brown and bubbly.

Cool the bars in the pan for at least 1 hour before slicing into squares.