Preheat the oven to 400° F. Bring a large pot of water to a boil.
Boil the sweet potatoes until tender, about 10-12 minutes. Drain and return to the pot with the heat OFF.
Pour in the remaining ingredients for the mash and blend with an immersion blender. (You can also transfer to a mixer, blender, or food processor, or simply mash by hand). Place in an 8x8 or 2-quart baking dish.
For the streusel, pulse the pecans a few times in a food processor or roughly chop with a sharp knife. Mix with the coconut sugar, coconut oil, cinnamon, and nutmeg and sprinkle over the sweet potatoes.
Bake for 10-15 minutes, until the top is bubbly.