In a 4 quart pot, combine the diced apples, lemon juice, pumpkin pie spice, brown sugar, white sugar, salt and 1/4 cup of water and stir. Cook on medium heat for about 10 minutes until the apples have softened, stirring occasionally. If all the liquid cooks off too quickly and the apples are not soft yet, add 1/4 cup more water to the pot.
Combine 1 tbsp of water and cornstarch in a small bowl and whisk with a fork. Add the cornstarch slurry to the apples and stir until the mixture thickens. Remove from heat and stir in vanilla extract and pumpkin puree. Allow to cool.
For the crisp topping, combine the brown sugar, oats, flour, pumpkin pie spice, and cubed butter in a medium bowl. Use 2 forks to mash the cold butter into the oats mixture until it resembles coarse crumbs.
Once the apple mixture has cooled, remove the CAULIPOWER cauliflower crust from the freezer. Spread the pumpkin-apple filling onto the crust, leaving a slight 1/2 inch border around the edges. Spread the oat mixture over the apples to the edge of the pizza. (Any leftover oat mixture can be frozen for a second use!)
Cook the "pie" directly on the middle oven rack for 12-15 minutes or until the crust and topping are golden brown and the apples are warm.
Serve with optional caramel sauce and whipped cream. Enjoy!!