• Adjust oven rack to middle position and preheat oven to 375°F.
• Spray an 8x8-inch (2-quart) baking dish with nonstick spray.

For the Streusel Topping

• In a medium bowl, combine the flour, oats, brown sugar, granulated sugar, cinnamon, and salt. Mix well. Add the butter and use a fork or pastry blender to cut it into the flour mixture. The mixture should be crumbly with some large pieces. Try not to overmix. Set aside.
  ¾ cup all-purpose flour, 1 cup old-fashioned oats, ½ cup brown sugar, ¼ cup granulated sugar, 1 teaspoon ground cinnamon, ⅛ teaspoon kosher salt, 10 tablespoons unsalted butter

For the Fruit Filling

• In a large bowl, gently mix together blueberries, strawberries, granulated sugar, flour, cinnamon, lemon juice, and salt.
  3 cups fresh blueberries, 3 cups chopped fresh strawberries, ½ cup granulated sugar, ¼ cup all-purpose flour, ⅛ teaspoon kosher salt, 1 tablespoon freshly squeezed Lemon juice

Assembly

• Pour the fruit mixture into the prepared baking dish and sprinkle the streusel mixture evenly over the top.
• Bake 30-35 minutes, or until golden brown and bubbly around the edges.
• Transfer to a cooling rack and cool 15-20 minutes before serving.