Heat the oven to 425°F. Boil the sweet potato for 10–12 minutes, until tender.

Mash it with the black beans, lime juice, chili powder, and salt.

Warm the tortillas in a damp towel for 30 seconds so they bend without cracking.

Add 2 tablespoons of filling to each tortilla. Roll tightly and place seam-side down on a baking sheet.

Brush with oil. Bake for 18–22 minutes, turning once, until crisp.