Preheat the grill. In a medium bowl, mash the black beans, 1 tablespoon olive oil, and garlic powder with a potato masher or fork until very creamy. Gently mix the black bean mixture with the ground beef. Season the mixture liberally with salt and pepper. Divide the mixture into 8 equally portioned thin patties. Using a pastry brush, lightly coat the outside of the patties with mustard. Lightly brush the grill with the oil and place the burgers on the hot grill. Cook the burgers until a golden crust is formed, about 1 to 2 minutes per side. Slice the mini buns in half and brush with the remaining oil. Place the buns on the grill until nicely toasted with grill marks. Serve the sliders on the toasted hamburger buns, topped with crunchy Grilled Crunchy Coleslaw.
Grilled Crunchy Coleslaw:
Preheat a grill. Place the cabbage wedges on a baking sheet, and drizzle with the vegetable oil on both sides. Sprinkle with sugar, salt, and pepper, and then toss to coat. Grill the cabbage for 4 minutes each side, or 8 minutes total, turning once or until the edges begin to wilt, but the bulk of the cabbage remains crunchy. Remove the cabbage from the grill and allow to cool a few minutes. Meanwhile, make the vinaigrette in a medium bowl by whisking the orange zest, Dijon mustard, and orange juice with the olive oil until it emulsifies. Add salt, and pepper, to taste. Chop the grilled cabbage, removing the core, and place in the bowl with the dressing. Add the parsley and green onion and toss to coat.