Preheat the oven to 375ºF. Prepare the crumble topping by mixing together the flour, brown sugar, butter, chopped pecans, and cinnamon. Mix the ingredients together until it looks like a crumbly mixture. Refrigerate the topping until ready to use.
Add the mashed sweet potato to a large bowl along with the eggs, brown sugar, vanilla, nutmeg, cinnamon, salt, and baking powder. Stir until everything is evenly combined and mostly smooth. It's okay if there are a few lumps of sweet potato.
Pour the milk into the bowl with the sweet potato mixture and stir or whisk to combine. Add the rolled oats and stir to combine again.
Coat the inside of a 2 quart baking dish lightly with non-stick spray. Pour the oatmeal mixture into the dish. Sprinkle the prepared pecan crumble topping over the oatmeal mixture.
Bake the oatmeal in the fully preheated oven for 45 minutes or until the pecan crumble topping and edges of the oatmeal are slightly browned. Serve immediately or refrigerate for later. Can be eaten hot or cold.
*1 lb. fresh sweet potato should yield about 2 cups once mashed. If you have slightly more or less than 2 cups the recipe will still work fine. Use your favorite method for cooking the sweet potato (boiling, baking, or microwaving). The total time for this recipe does not include cooking the sweet potatoes as different methods take different amounts of time. I boiled my potatoes, which added about 15 minutes to the total recipe time.