In a large mixing bowl, toss the diced sweet potatoes with olive oil, cumin, smoked paprika, garlic powder, salt, and pepper. Spread the sweet potatoes in a single layer on a baking sheet lined with parchment paper. Roast in the preheated oven for 25-30 minutes, turning halfway through, until crispy and golden brown.
In a small saucepan over medium heat, warm the black beans until heated through, about 5 minutes. Stir occasionally, and season with salt and pepper to taste.
While the sweet potatoes and black beans are cooking, warm the corn tortillas by heating them in a dry skillet over medium heat for about 30 seconds on each side, or wrapping them in foil and placing them in the oven for the last 5 minutes of the sweet potatoes' cooking time.
To assemble the tacos, place a couple of spoonfuls of roasted sweet potatoes and a scoop of black beans on each warm tortilla. Top with shredded red cabbage, slices of avocado, and chopped cilantro.
Serve the tacos with lime wedges on the side for squeezing on top just before eating. Enjoy your crispy black bean and sweet potato tacos!