Strain pumpkin in a fine mesh strainer until all liquid is gone. Pumpkin should be thick. Prepare 9-inch round spring form pan by placing parchment paper on the bottom and sides of pan. Spray or use thin brush to coat with oil. Melt chocolate and set aside to cool. Place ricotta cheese in large bowl and blend until smooth. Add melted chocolate, pumpkin, spices and combine until smooth, scraping sides. In another bowl, whip cream until stiff peaks form and then gently fold into ricotta mixture.
To assemble, arrange half the cookies in a slightly over-lapping pattern to cover bottom of pan. Spoon half of the ricotta mixture evenly on top of cookies. Cover with the remaining cookies and top with remaining mixture, smooth top. Cover with plastic wrap and refrigerate at least 12 hours or up to 2 days. Release sides of pan and remove parchment paper. Using a metal spatula lift/slide cake and remove paper and set on serving platter. Shave chocolate over top of cake using a vegetable peeler. Use knife dipped in hot water to slice cake. Serves 10-12.