Preheat the oven to 400ºF. Line a baking sheet with aluminum foil and set aside.
In a large skillet, add the sweet potato and oil. Saute over medium heat for 1 - 2 minutes, then add water. Cover the pan and allow sweet potatoes to steam until softened about 10 minutes.
Transfer the sweet to a bowl and return the pan to the heat. Add onion and cook until softened, about 5 minutes. Once softened, add black beans, half of the sweet potatoes, spices and salt and saute until beans are warm, about 3 minutes. Remove from heat.
Mash the remaining sweet potatoes and assemble the taquitos.
Place a tortilla on a flat surface. Spread 1 tablespoon of mashed sweet potato on a third of the tortilla. Place 2 - 3 tablespoons of the filling on top of the sweet potato and roll tortilla tightly around the filling to form a small tube. Place tortilla seam side down on the baking sheet and repeat until all tortillas have been filled.
Place taquitos in the oven and bake for 25 - 30 minutes until the tortillas are nice and crispy. You may want to flip them over halfway through to avoid burning (depending on your tortillas).
While taquitos are cooking, prepare the sauce. Add all the ingredients into a blender, starting with 1/4 cup of water. Blend on high until smooth, adding more water as needed to thin.
When ready to serve, plate the taquitos with the dipping sauce and enjoy!