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

In a large mixing bowl, whisk together the flour, granulated sugar, light brown sugar, baking powder, and salt.

Add the chilled, cubed unsalted butter to the dry mixture and work it in until it resembles coarse crumbs.

Set aside 1½ cups of the crumb mixture for the topping. Stir in rolled oats into the remaining mixture and press it into the bottom of the pan.

Bake the crust for 15 minutes, until edges are lightly golden.

While the crust bakes, mix the filling ingredients together until strawberries are well-coated.

Spread the strawberry mixture evenly over the baked crust.

Crumble the reserved crumb mixture over the strawberry filling, pressing lightly to create an even layer.

Bake for an additional 40-45 minutes, until the streusel is golden brown and filling is bubbling.

Cool the bars in the pan for 2-3 hours, then refrigerate for another 2 hours.

If desired, prepare a glaze and drizzle it over the cooled bars.

Lift the bars from the pan using the parchment overhang and slice into squares.