Preheat oven to 450 degrees F.
Place the potatoes on a baking sheet lined with foil (for easier clean up). Liberally toss with 2 tablespoons olive oil, salt, pepper, garlic powder and paprika. Spread onto an even layer and roast for about 25 to 30 minutes or until golden brown and crispy.
Heat a large skillet over medium high heat with 1 tablespoon olive oil. Add the ground beef and cook, breaking down with the back of a spoon, until brown and crispy. Add the onions and garlic and cook for about 5 minutes more. Stir in the water, taco seasoning, tomato sauce, and cornstarch and black beans. Simmer on low until thick.
Top the potatoes with the cheese and place back in the oven until melted and heated through. Carefully remove from oven and top with beef mixture, sour cream, guacamole, scallions, tomatoes, and cilantro. Enjoy right away!
To make the guacamole, combine all of the ingredients in a large bowl and mash until completely incorporated.