1. Prepare the Filling
In a large bowl, combine pumpkin puree, diced apples, maple syrup, pumpkin pie spice, cinnamon, ginger, nutmeg, cornstarch, and lemon juice. Stir until well combined. The cornstarch helps thicken the filling beautifully. Pour the mixture into an 8×8 inch baking dish or a 9-inch pie plate.

2. Make the Crumble Topping
In a separate medium bowl, combine rolled oats, almond flour, whole wheat pastry flour (if using), chopped nuts, cinnamon, and salt. Mix well. Add the melted coconut oil, maple syrup, and vanilla extract. Stir with a fork until the mixture is crumbly and wet, resembling coarse sand. Ensure all dry ingredients are moistened.

3. Assemble and Bake
Evenly sprinkle the crumble topping over the pumpkin and apple filling in your baking dish. Place the dish on a baking sheet to catch any potential drips. Bake in a preheated oven at 375°F (190°C) for 35-40 minutes, or until the topping is golden brown and the filling is bubbly around the edges.

4. Cool and Serve
Remove the crumble from the oven and let it cool on a wire rack for at least 15-20 minutes before serving. This allows the filling to set and prevents it from being too runny. Serve warm, perhaps with a dollop of coconut whipped cream or a scoop of dairy-free vanilla ice cream.