Tender, smoky sweet potato is the star of these vegetarian tacos. A mashed black bean spread with onion holds everything in place. Serve with your favorite taco toppings.
Preheat oven to 450°F. Combine sweet potatoes, paprika, garlic powder, salt and 2 tablespoons oil in a large bowl; toss to coat. Spread on a large rimmed baking sheet and roast until tender and browned, about 25 minutes, flipping and tossing halfway through.
Heat the remaining 1 tablespoon oil in a large skillet over medium-high heat. Add onion; cook, stirring occasionally, until softened, about 5 minutes. Add beans; cook, stirring occasionally, until warmed through, about 2 minutes. Transfer 1/3 cup of the bean mixture to the baking sheet with the sweet potatoes; toss to combine.
Add 1/2 cup water to the remaining bean mixture in the skillet over medium-high heat; stir and mash the bean mixture with the back of a fork or a potato masher until it's almost smooth but some bean chunks remain. Remove from heat; stir in lime juice.
To serve, spread 1 1/2 tablespoons mashed bean mixture onto each tortilla and spoon 2 tablespoons sweet potato mixture over the bean mixture. Top evenly with queso fresco and sliced avocado. Add sour cream, salsa, pepitas and/or cilantro, if desired. Serve immediately with lime wedges.