Cook the potatoes: bring a large pot of water to boil over high heat. Peel and cube the sweet potatoes into about 1” cubes. Add the potatoes to the pot and gently boil for 20 - 30 minutes, until cooked through.
Make the topping: while the potatoes cook, make the crumble topping. In a small mixing bowl, stir together the oats, pecans, flour, and coconut sugar (or brown sugar). Press the coconut oil into the oats with your fingers until there are small (pea-sized) lumps. If using a flour besides almond flour, add a little at a time until the desired consistency is reached.
Preheat the oven to 350°F. Grease a 9” x 13” baking dish.
Mix the potatoes: drain the potatoes and then add them to a large mixing bowl. Add the vegan butter and mash by hand or with an electric mixer until no lumps remain. Stir in the milk, syrup, vanilla, cinnamon, nutmeg and salt into the potatoes.
Assemble: spread the sweet potato mixture into your greased baking dish. Sprinkle the crumble topping in an even layer on top.
Bake: bake for 40 - 45 minutes, until the crumble topping is golden brown and the potatoes are heated through. Serve warm, optionally topped with another drizzle of maple syrup.