For the crumbles: Combine the flour, baking powder, cinnamon, white and brown sugars and orange zest in a medium bowl; use your hands to help crumble and distribute the brown sugar. Stir in the melted butter. With your hands, squeeze the mixture to make large clumps. Refrigerate until firm, about 20 minutes. Break into crumbles and chill until ready to use.
For the oatmeal: Preheat the oven to 350 degrees F.
Spread the oats on a baking sheet and bake, shaking the pan once or twice, until light golden brown and toasty-smelling, about 8 minutes. Remove and let cool slightly.
Grease an 8-inch square baking dish with butter.
In a medium bowl, combine the toasted oats, brown sugar, cane sugar, pumpkin pie spice, allspice and salt. In a separate bowl, whisk together the pumpkin puree, milk, eggs, vanilla extract and raisins. Stir the dry mixture into the wet; the mixture will be loose. Pour into the prepared baking dish.
Bake until just barely set, 20 to 25 minutes. Sprinkle the cinnamon crumbles on top, return to the oven and bake until the oatmeal is firm and the crumbles are golden brown, about 20 minutes longer. Remove and let cool for 10 minutes.
Scoop into bowls, top with Greek yogurt and drizzle with warm maple syrup.