01 - Preheat oven to 350°F. Lightly grease a 2-quart baking dish.
02 - Place sweet potato chunks in a large pot, cover with cold water, and bring to a boil. Cook until tender, approximately 15–20 minutes. Drain thoroughly.
03 - Transfer sweet potatoes to a large bowl and mash until smooth.
04 - Add milk, melted butter, brown sugar, eggs, cinnamon, nutmeg, ginger, allspice, salt, vanilla extract, and orange zest if using. Stir until mixture is creamy and well combined.
05 - Evenly spread the sweet potato mixture in the prepared baking dish.
06 - In a medium bowl, combine pecans, oats, brown sugar, melted butter, cinnamon, and a pinch of salt. Mix until the topping is thoroughly coated.
07 - Sprinkle the pecan topping evenly over the sweet potato base. Bake for 35 to 40 minutes, until set and golden brown on top.
08 - Allow to cool slightly before serving.