Sprinkle the steak with 2 teaspoons chili powder and 3/4 teaspoon salt. Heat 1/2 tablespoon olive oil in a large skillet over medium-high heat. Add the steak; cook about 5 minutes per side for medium rare. Meanwhile, make the slaw: Toss the cabbage with the lime juice, mayonnaise, 2 tablespoons cilantro, the remaining 1 teaspoon chili powder, and salt to taste. Chill until ready to serve. Transfer the steak to a cutting board and let rest 10 minutes. Meanwhile, heat the remaining 1/2 tablespoon olive oil in the same skillet over medium heat. Add the onion and tomato paste and cook, stirring, until the onion is soft, 2 to 3 minutes. Add the chicken broth and beans and bring to a simmer. Coarsely mash the beans with a spoon; continue cooking until slightly thickened, about 4 more minutes. Add the remaining 2 tablespoons cilantro and salt to taste. Slice the steak; top with the black beans and serve with the slaw.