Preheat the oven to 350 degrees.
Make the crust: In a large bowl, combine the oat flour, almond meal, oats, sugar, and salt. Add the butter and use a pastry cutter to mix it all together. Add the 2 T. of water and mix it until it comes together as a thick dough.
Place the dough into an eight inch square baking dish and use your hands to spread it out and pat it down. Put it into the oven to bake for 10 minutes while you make the pumpkin filling and crumb topping. Set the empty bowl aside so that you can mix the crumb topping in it as well.
Make the pumpkin filling: If not using eggs, mix 2 T. of ground flax seed meal and 6 T. of water in a small mug and let it sit for about 5 minutes, or until it gels up. In a large bowl, combine the eggs OR flax seed gel, pumpkin puree, yogurt, vanilla, salt, and spices. Mix together with a spoon. Set aside.
Make the crumb topping: In the same bowl that you made the crust in, combine the oats, oat flour, light brown sugar, cinnamon, salt, and butter. Combine with the pastry cutter until the mixture looks like a crumbly topping. There should be some larger balls of buttery crumbs in the mix.
Assemble the dessert: Spread the pumpkin filling over the crust, smoothing it out with a spoon. Sprinkle the crumble topping all over the top. Bake at 350 degrees for about 35-40 minutes. If the crumb topping starts to get too brown, cover it with a piece of foil. Let cool fully before serving.