Extra-virgin olive oil, as needed
1 small onion, chopped
2 garlic cloves, chopped
Kosher salt and freshly ground black pepper, to taste
2 or 3 medium sweet potatoes, washed
3 teaspoons chili powder
1 teaspoon ground cumin
½ teaspoon crushed red pepper flakes
Corn tortillas, fresh cilantro, limes, avocado and pickled onions, for serving
1. Using a box grater, grate the sweet potatoes (no need to peel them). You can also use a food processor fitted with a grater attachment.
2. Meanwhile, heat the olive oil in a medium skillet over medium heat. Add the onion and garlic, and cook until fragrant and starting to soften, about 3 minutes. Season to taste with salt and pepper. Add the grated sweet potato, chili powder, cumin and red pepper flakes, then cover and cook until soft, 5 to 7 minutes.
3. Serve the filling inside warm corn tortillas with a squeeze of fresh lime juice, fresh cilantro, avocado and pickled onions.