Preheat oven to 350 F. Pierce sweet potatoes several times with a fork all over and wrap each with aluminum foil. Bake in preheated oven until tender, 1 hr. – 1 ½ Remove from oven and let cool.
While sweet potatoes bake, place the gingersnap cookies in the bowl of a food processor and process until they are finely ground. You should have about 2 cups. Add the walnuts and sugar; pulse to combine. Add the butter and pulse briefly again until everything is mixed together.
Pat the crust into a deep 9-inch pie plate, and up the sides. Bake for 10-15 minutes (at 350 F), until firm and slightly darkened. Set aside to cool.
Peel cooled sweet potatoes and discard skins. Process yams in a food processor until mixture is smooth and forms a ball, about 1 minute.
Place yam mixture into a large bowl and whisk in brown sugar, evaporated milk, 1/2 cup butter, eggs, vanilla, ube flavoring (optional), 1/2 teaspoon cinnamon, five-spice, salt, and nutmeg until smooth and combined.
Pour sweet potato mixture into prepared gingersnap pie shell. Bake in preheated oven until filling is set, about 50 minutes.
Meanwhile, stir together oats, pecans, coconut, remaining 2 tablespoons brown sugar, remaining 2 tablespoons butter, and remaining 1/4 teaspoon cinnamon in a bowl. Set aside.
Remove pie from oven; sprinkle center of pie with oat mixture. Return to oven; bake at 350°F until topping is lightly browned, about 10 minutes. Transfer pie to a wire rack to cool completely, about 4 hours.
To make maple whipped cream: combine all ingredients together and using a hand mixer, stand mixer, food processor or whisk and lots of elbow grease, whip until medium peaks form.