Preheat the oven to 375°F. Spray a 9-by-9-inch baking pan with nonstick spray. Press in a piece of aluminum foil that fits up to the rim, then press in a piece of parchment paper of the same size.

In a large bowl, stir together the oats, flour, tapioca starch, sugar, walnuts, salt, baking soda, and cinnamon until well combined. Add the shortening and combine, using your hands, until the mixture is homogeneous and holds together when pressed.

Firmly and evenly press 3⁄4 of the mixture into the prepared pan. Spread the raspberry jam evenly onto the dough, leaving a 1⁄2-inch border on all sides of the pan (to aid in unmolding). Top with the frozen fruit. Sprinkle the remaining crumble mixture over the fruit, leaving some fruit peeking through.

Bake for 35 minutes, rotate the pan, and bake for another 10 to 15 minutes, until evenly golden brown and well set. Chill completely before cutting and serving.