Prepare the crust: Preheat the oven to 350ºF. Line an 8-inch round spring-form pan or pie plate with parchment paper or spray with nonstick spray. In a small bowl, whisk together the sugar, water, vanilla, and stevia until the sugar dissolves. Add the coconut oil and whisk again to blend (it may curdle a bit; this is okay). Mix in the flaxseeds. In a medium bowl, sift together the flour, cocoa powder, baking powder, xanthan gum, and sea salt. Add the wet ingredients and stir to blend (it will be a soft and slightly sticky dough). Spread or pat the dough into the pan to cover the bottom. Place in the refrigerator to firm up while you prepare the filling.
Prepare the filling: Place the cashews, tofu, pumpkin, coconut sugar, coconut butter, stevia, cornstarch, lemon juice, vanilla, cinnamon, ginger, allspice, nutmeg, and salt in a high-powered blender (such as a Vita Mix) and blend until silky smooth. You may need to use the tamper to push the ingredients down into the blades. Scrape the blender sides a few times to ensure that everything is mixed in. The mixture will be thick. Remove ¾ cup of the pumpkin mixture to a small bowl and stir in the cocoa powder and agave. Set aside.
Pre-bake the crust: Remove the crust from the refrigerator. Once cold, the crust should firm up (if it isn’t quite cold yet, return to the fridge for 10 minutes or so, until it is firm). Bake the empty crust in the preheated oven for 12-15 minutes until it’s dry on top and starting to puff a bit. Remove from the oven.
Pour the pumpkin mixture into the partially baked crust. Using a tablespoon, place blobs of the chocolate mixture on top of the pumpkin base, leaving some parts uncovered. Use a dull knife or thin spatula to marble the 2 batters by drawing figure-eights gently through the mixture (take care not to cut the crust underneath).
Wearing oven mitts, grab the pan with one hand on each side and quickly rotate the pan to the left, then the right several times to help flatten out the surface of the cheesecake. Place the cake back in the oven and continue to bake for 45-55 minutes, rotating the pan once about halfway through, until the top is well browned and the sides just begin to pull away from the pan. A tester inserted about 1/3 of the way toward the center should come out clean.
Allow to cool completely before covering and refrigerating for 6 hours or up to 24 hours before serving.