Roast sweet potatoes – Preheat oven to 220°C (425°F). Toss cubes with oil, cumin, paprika, chili powder, garlic powder, salt, and pepper. Spread on a baking sheet and roast 20–25 minutes, flipping once, until crisp and golden.
Warm beans – Heat beans in a small skillet with a splash of water, pinch of cumin, and salt. Stir until warmed through.
Toast tortillas – Warm tortillas in a dry skillet or over direct flame for 10–15 seconds per side. Keep wrapped in a towel.
Assemble tacos – Layer tortillas with black beans, roasted sweet potatoes, avocado slices, red cabbage, and pickled onions.
Finish & serve – Garnish with cilantro and fresh lime juice. Serve immediately.