Make the taco shell: Line a baking sheet with a paper towel. Pour enough oil into a large Dutch oven to reach a depth of 2 inches and heat until a deep-fry thermometer reaches 350˚. Working with 1 tortilla at a time, fry, flipping often until the tortilla is light golden, 45 seconds to 1 minute. Using tongs, push down on the center of the tortilla, so the outer edges flare and puff up. Continue to fry until golden brown and puffy, 1 minute more. Remove from the oil and place upside down over a glass cup set over the prepared baking sheet; season with salt. Repeat with the remaining tortillas.
Make the crema: In a small bowl, combine the sour cream and spices. Stir. Let sit at least 15 mins for flavors to combine.
Make the black beans: In a small saucepan over medium heat, add the olive oil. When the olive oil is hot, add the onions and season lightly with salt. Cook, stirring often, until soft but not brown, 4 to 5 minutes. Add the beans and water, and cook for 8 to 10 minutes. Stir in the oregano and keep warm on low heat.
Make the grilled tomatoes: Prepare a medium-hot fire in a charcoal grill or heat a gas grill to medium-high heat. Alternatively, place a grill pan over medium-high heat. Brush the tomatoes with the oil and grill, flipping occasionally, until the tomatoes have blistered, 2 to 4 minutes. Season with salt, roughly chop and set aside.
Make the skirt steak: In a small bowl, combine the paprika, cumin, salt, onion and garlic powders, and black pepper. Rub the steak with the seasoning.
Grill the steak, flipping once, until it's lightly charred and cooked to preferred doneness, 3 minutes per side for medium rare. Transfer to a cutting board and let rest for 10 minutes before slicing.
Assemble the taco salad: Drain the black beans and place them in a large bowl. Add the cabbage, grilled tomatoes, radishes, cilantro and mint. Add the olive oil, season with salt and toss.
Divide the cabbage mixture among the 4 taco shells. Top each taco shell with the steak, avocado slices, jalapeño or serrano rounds, and Cotija. Garnish each shell with a lime wedge and serve with the crema.
