Step 1

Whisk 2 tablespoons rice wine vinegar, sesame oil, miso, ginger, and red pepper flakes in a small bowl until smooth. Set aside.

Step 2

Place oven rack 6 inches from broiler. Preheat broiler and coat a baking sheet or broiler pan with 1 tablespoon olive oil. Arrange fish on pan and brush generously with miso mixture. Broil until opaque in centers and browned on top, 7–8 minutes.

Step 3

While fish cooks, bring ¼ cup water to boil in a medium pan. Add bok choy, cover, and cook for 3 minutes; remove cover and let water boil off. Remove from heat. Add remaining 2 tablespoons rice wine vinegar and 1 tablespoon olive oil, plus soy sauce, lemon juice, and 1 tablespoon chives; combine well.

Step 4

Divide bok choy mixture among four plates. Place broiled fish on top of each. Garnish with remaining chives, and sprinkle with freshly ground black pepper to taste and black sesame seeds, if desired.