Preheat your oven to 350°F (177°C) and line a 9x13-inch baking pan with parchment paper.

In a large mixing bowl, combine all-purpose flour, granulated sugar, light brown sugar, baking powder, and salt.

Cut in chilled, cubed unsalted butter until the mixture resembles coarse crumbs.

Reserve one cup of the mixture for topping, then add rolled oats to the remaining mixture and press into the bottom of the prepared pan.

Par-bake the crust for 15 minutes until lightly golden.

In a separate bowl, mix diced strawberries, granulated sugar, lemon juice, cornstarch, jam, and vanilla extract for the filling.

Spread the strawberry filling over the warm crust evenly.

Crumble the reserved topping mixture over the strawberry layer and lightly press down.

Bake for an additional 40-45 minutes until golden brown and filling bubbles slightly.

Allow to cool at room temperature for 2-3 hours before slicing.

Prepare an optional glaze and drizzle over bars before serving.

Lift bars from the pan using parchment overhang, slice, and serve.