Preheat the oven to 425°. Cube the yams then toss with 2 tablespoons of the oil and 3 teaspoons chili powder. Spread on a rimmed baking sheet, and roast for 25 minutes, turning 2-3 times during cooking.
Blend the soaked cashews, water, yeast, lime juice, cumin, chili powder, chile in adobo, garlic clove and sea salt in a high-speed blender until very smooth. Add more water to achieve desired consistency.
Over medium heat, sauté the black beans and spinach in 1 tablespoon of oil until the spinach is wilted.
Meanwhile, once the yams are done, move to a bowl and using a fork or masher, mash to desired consistency.
Heat tortillas. To assemble tacos, scoop a couple spoonfuls of the mashed yams onto tortillas then top with spinach and black bean mixture. Drizzle with cashew sauce, and garnish with cilantro, avocado and any other toppings you are using. Serve immediately.