Toss diced sweet potatoes with olive oil, cumin, smoked paprika, chili powder, salt, and pepper. Spread on a baking sheet in a single layer.
Roast sweet potatoes for 25-30 minutes, turning halfway through, until fork-tender and slightly caramelized with golden-brown spots.
While sweet potatoes roast, warm the tortillas. Wrap in foil and place in oven during last 5 minutes, or heat in a dry skillet for 30 seconds per side.
In a small pot, heat black beans over medium heat until warmed through, about 3-5 minutes.
Assemble tacos by layering 2-3 tablespoons sweet potatoes, 2 tablespoons black beans, red onion, cilantro, and avocado slices on each tortilla.
Squeeze fresh lime juice over the top and add salsa or hot sauce if desired. Serve immediately.
Notes
Use corn tortillas for gluten-free option or whole wheat tortillas for added fiber.
Sweet potatoes can be prepped ahead and stored in the fridge for up to 4 days for quick assembly.
Cut sweet potatoes into uniform 1/2-inch pieces for even roasting and caramelization.
Roasted sweet potatoes can be frozen for up to 3 months for easy meal prep.
One 15 oz can of black beans yields approximately 1.5 cups drained beans.