Heat a medium pot of water to boiling on high. Wash and dry the fresh produce. Cut the sweet potato into ¼-inch-thick rounds. Cut off and discard the root ends of the scallions; thinly slice on an angle, separating the white bottoms and green tops. Peel and finely chop the ginger. Cut off and discard the ends of the radishes; thinly slice into rounds. In a bowl, combine the mayonnaise and up to half the gochujang, depending on how spicy you’d like the dish to be; season with salt and pepper to taste.

To make the batter, in a large bowl, whisk together the tempura mix and ¼ cup of cold water until smooth; season with salt and pepper. In a large pan (nonstick, if you have one), heat a thin layer of oil on medium-high until hot. Once the oil is hot enough that a drop of batter sizzles immediately when added to the pan, working in batches if necessary, coat the sweet potato in the batter (letting any excess drip off). Carefully add to the pan in a single layer and cook 4 to 6 minutes per side, or until lightly browned and crispy. (If the pan seems dry, add a drizzle of oil between batches.) Transfer to a paper towel-lined plate; immediately season with salt and pepper. Carefully discard any excess oil. Wipe out the pan.

While the sweet potato cooks, rest a strainer (or colander) over the pot of boiling water, making sure the water doesn’t reach the bottom of the strainer. Working in batches if necessary, place the buns in the strainer; cover with the lid of the pot. Steam 3 to 5 minutes, or until softened and puffy. Carefully transfer to a work surface.

Using your hands, separate the sliced beef; pat dry with paper towels. Season with salt and pepper. In the same pan, heat 2 teaspoons of olive oil on medium-high until hot. Add the seasoned beef in a single layer. Cook, without stirring, 1 to 2 minutes, or until browned. Add the white bottoms of the scallions, ginger, black bean sauce, and as much of the remaining gochujang as you’d like, depending on how spicy you’d like the dish to be. Season with salt and pepper. Cook, stirring frequently, 1 to 2 minutes, or until thoroughly combined and the beef is just cooked through. Turn off the heat; season with salt and pepper to taste.

Gently open each steamed bun; spread with a thin layer of the spicy mayonnaise. Divide the cooked beef and radishes among the buns. Transfer ⅔ of the assembled buns and ⅔ of the sweet potato tempura to serving dishes (you will have extra buns and tempura). Garnish the buns with the green tops of the scallions. Enjoy!