Preheat oven to 350°F. Line an 8x8-inch pan with parchment paper or foil and grease lightly.

In a medium bowl, toss together raspberries and tapioca starch. Let stand while you prepare the crust.

In large bowl, combine the rest of the ingredients except the chocolate chunks. Stir until combined.

Reserve 1 cup of crumb mixture for the topping. Press remaining crumb mixture evenly into the bottom of greased pan. Bake at 350°F for 10 minutes.

Remove partially baked crust from the oven. Sprinkle chocolate over the crust. Evenly distribute raspberries on top. Top with remaining crumb mixture.

Return to oven and bake for another 30-35 minutes or until bubbling and lightly browned. Let cool completely before cutting into 16 squares.