4 garlic cloves, divided
1/2 cup balsamic vinegar
3 tablespoons Dijon mustard
1/2 cup plus 2 tablespoons extra-virgin olive oil, divided
2 tablespoons chopped fresh oregano leaves, divided
1 1/2 teaspoons kosher salt, divided
3/4 teaspoon freshly ground black pepper, divided
1 (1 1/2-pound) skirt steak, cut crosswise into 2 equal pieces
1 bunch broccolini (about 10 ounces), trimmed, halved lengthwise (quartered lengthwise if large)
1 (15-ounce) can white beans, rinsed, drained

Finely chop 2 garlic cloves. Place in a large bowl or shallow baking dish, then whisk in vinegar, Dijon, 1/2 cup oil, 1 T. oregano, 1 tsp. salt, and 1/2 tsp. pepper. Reserve 1/4 cup vinaigrette for serving; add steak to remaining vinaigrette and turn to coat. Let marinate at least 15 minutes or up to 1 hour. Meanwhile, preheat broiler and thinly slice remaining 2 garlic cloves. Toss broccolini, remaining 2 T. oil, 1 T. oregano, 1/2 tsp. salt, and 1/4 tsp. pepper on rimmed baking sheet. Broil 5 minutes, then remove from oven. Add beans and garlic and toss to combine. Set wire rack on top of broccolini mixture. Place steak on rack; discard vinaigrette. Broil steak, turning halfway through, until cooked to desired doneness, about 3 minutes per side for medium-rare. Let steak rest 5 minutes. Meanwhile, transfer broccolini mixture to a medium bowl and toss with 1 T. reserved vinaigrette, then divide among 4 plates. Thinly slice steak against the grain and serve with broccolini mixture and remaining vinaigrette alongside.