Preheat the oven to 350°F and grease or line a 5 x 9-inch loaf pan with parchment paper.

Peel the sweet potatoes, chop them into chunks, and cook in simmering water until very soft. Drain well and mash until smooth. Alternatively, bake the sweet potatoes until tender, then peel and mash. Allow the puree to cool to room temperature.

In a small bowl, combine the streusel ingredients: brown sugar, flour, and cinnamon. Add the oil and water, then mix or crumble with your fingers to create small clumps. Set aside.

In a medium bowl, stir together the gluten-free flour, baking powder, salt, cinnamon, ginger, and nutmeg until evenly combined.

In a large bowl, whisk together the sweet potato puree, oil, and low-carb sweetener until smooth. Add the oat milk and whisk until well combined.

Gradually add the dry ingredients to the wet mixture, stirring gently until no lumps remain.

Pour the batter into the prepared loaf pan, spreading it evenly. Sprinkle the streusel mixture over the top in an even layer.

Bake for 50-60 minutes, or until a toothpick inserted into the center comes out clean.

Allow the loaf to cool in the pan for 10 minutes before transferring it to a cooling rack. Let it cool completely before slicing and serving.