Preheat oven to 400. Using a fork, poke a few holes in the top of each sweet potato. Place on a baking sheet or in a baking dish and roast until fork tender, about 60 minutes, or until fork tender.
Boil water and place cashews in a small bowl. Pour water over them and allow cashews to soak for 15-30 minutes to soften (or overnight for best results). Drain the cashews in a colander.
In a food processor or blender, combine all of the ingredients for the cashew nacho sauce and blend until smooth, adding water (or broth) as you go to thin it out. You'll need at least 1/4-1/2 cup liquid, but add it in increments as to not water it down too much.
In a medium skillet, sauté the black beans and corn with salt & pepper to taste to warm them.
When potatoes are done roasting, remove from the oven, let cool for a few minutes and slice in half (either fully or keep in a "boat" shape depending on serving size). Use a fork to gently mash the inside of the sweet potatoes.
Top with taco ingredients and drizzle the cashew nacho sauce on top.