Preheat oven to 400° F. Line a rimmed, large baking sheet with a piece of parchment paper for easy cleanup.

In a large bowl, toss sweet potatoes with a tablespoon of the oil and ground cumin. Season them with salt and pepper, to taste. Arrange them on the rimmed baking sheet. Roast for 20-25 minutes or until brown and slightly crisp around the edges.

While the cubes of sweet potato roast, heat water, vinegar, sprinkle of salt, and sugar in a small saucepan to a steady simmer.

Place red onion in a glass jar. Pour the vinegar mixture over the onions. Cool for 10-15 minutes at room temperature and then transfer to the refrigerator to chill.

Meanwhile, combine avocado, sour cream, garlic, and lime juice in a high-speed blender. Blend until completely smooth and creamy.

Assemble the tacos by spreading a dollop of avocado sauce on the warmed tortillas. Add the roasted sweet potato cubes, hearty black beans, pickled red onion, and fresh parsley. Feel free to add an extra topping, if desired. Enjoy!