Heat your oven to 350 and prepare a 9 X 12 baking pan by giving it a light coating of vegetable spray.
In a medium bowl combine the cake mix with half a cup of melted margarine. Stir until a pasty dough is form. Press dough into the bottom of prepared baking pan. Use your fingers to press the dough across the pan evenly.
Prepare Crumble Topping by combing the flour, oats, brown sugar, cinnamon, salt, vegan butter (or coconut oil) in a food processor. Pulse for several seconds until well combined. Scoop this out of the food processor into a bowl. Set aside. And don't clean out that food processor bowl just yet. I like to go from Crumble Topping straight to the Pumpkin Sauce - any minimal leftover ingredients in that food processor bowl will be just fine for the pumpkin sauce as well. Waste not, want not - that's what my mom loves to say!
Next, prepare the pumpkin sauce by combining the can of pumpkin, chickpeas, and plant-based milk in a food processor. Pulse for several seconds until the chickpeas are ground up and the mixture looks smooth. Add the ground flax seed (optional), cornstarch, sugar, and spices. Pulse several seconds until everything is combined.
To assemble your Pumpkin Crisp, pour the Pumpkin Sauce evenly over the cake batter crust. Then top that with the Crumble Topping, making sure it is equally distributed.
Bake for 40 minutes until the center is set and the topping is golden brown.
Remove from oven and set aside to cool. Serve while still warm with a nice dollop of your favorite non-dairy ice cream