2 pounds sweet potatoes (about 4 medium sweet potatoes), peeled and cut into 1-inch cubes
3 tablespoons olive oil, divided
1 onion, finely diced
2 teaspoons ground cumin
2 teaspoons chili powder
½ teaspoon salt
¼ teaspoon cayenne
2 (15-ounce) cans refried black beans
1 cup lightly packed cilantro leaves
8 corn tortillas
4 ounces crumbled feta cheese
2 avocados, diced
Preheat the oven to 425ºF.
Toss the prepared sweet potatoes with 2 tablespoons of the olive oil, salt, and cayenne. Spread the potatoes on a large, rimmed baking sheet in a single layer. Bake in the preheated oven for 30 to 40 minutes, tossing once about halfway through the cooking time, until the sweet they are tender and beginning to brown.
Heat the remaining tablespoon of oil in a large saucepan over medium heat. Add the onions and cook, stirring, for about 5 minutes, until the onions are soft. Add the cumin and chili powder and continue to cook, stirring, for about 30 seconds more. Add the beans and stir to mix well. Reduce the heat to low and cook, stirring occasionally, until the beans are heated through, about 5 minutes.
Warm the tortillas one at a time in a skillet over medium-high heat.
To make the tacos, spoon some of the black beans in the center of each tortilla. Spoon the sweet potatoes over the beans, and then top with avocado, feta cheese, and any other toppings you like. Serve immediately.