Preheat the oven to 425°F. Toss the diced sweet potatoes with oil, cumin, chili powder, salt, and pepper. Spread on a sheet pan and roast for 25 minutes, flipping halfway.
In a small bowl, toss the cabbage with lime juice, oil, and salt. Let sit while the potatoes roast.
In a blender or food processor, combine the cilantro, lime juice, garlic, oil or tahini, and water. Blend until smooth and drizzle-able, adding more water as needed.
Heat the tortillas on a dry skillet or open flame until soft and pliable.
Layer each tortilla with roasted sweet potatoes, cabbage slaw, a drizzle of cilantro sauce, and any extra toppings you like.