Thaw 2 cups of frozen raspberries in a bowl for about 10-15 minutes. Once thawed, carefully drain and pat dry with paper towels.

In a medium bowl, combine the dried raspberries with ⅓ cup granulated sugar, 2 tablespoons of all-purpose flour, 1 tablespoon of cornstarch, and 2 teaspoons of lemon juice.

Preheat your oven to 350°F (175°C) and line an 8x8-inch baking pan with parchment paper. In a large bowl, stir together 1 cup old-fashioned oats, 1 cup all-purpose flour, ½ cup brown sugar, 1 teaspoon baking powder, and ¼ teaspoon sea salt.

Press the remaining streusel mixture into the prepared baking pan and bake for 10-12 minutes until lightly golden.

Pour the raspberry filling over the baked base and sprinkle with the reserved streusel mixture.

Bake the assembled bars for an additional 25-30 minutes until the top is golden brown and the filling is bubbly.

Let the bars cool in the pan for 30 minutes, then refrigerate for at least 2 hours before slicing.