Preheat the oven to 375 degrees Fahrenheit. Toss the cubed sweet potatoes with the olive oil and most of the BBQ sauce (reserving 2 tablespoons), and add them to a glass baking dish. Cover the dish with foil, and cook for 30 minutes. Uncover the dish, stir the sweet potatoes, and cook for another 25-35 minutes or until tender. Add more barbecue sauce if desired.
Meanwhile, warm the black beans in a small saucepan or skillet, along with the remaining 2 tablespoons of BBQ sauce. Add salt to taste. (You can also stir them in with the sweet potatoes and heat them up in the oven to save a pan).
LEFTOVERS: Make the full recipe, but only prep one avocado. Save half of everything, and serve with a freshly-cut avocado when ready to eat. Leftover sweet potatoes and black beans will keep for several days in the refrigerator.
NUTRITION: Nutrition is calculated with corn tortillas and using all of the toppings.