Thaw fish, if frozen. Rinse fish; pat dry with paper towels. For dressing, in small bowl combine vinegar and shallots. Whisk in mustard. Whisking constantly, add oil in a steady thin stream. Stir in anchovy; season to taste with salt and pepper. Remove 1 tablespoon dressing to brush fish; set aside remaining dressing until ready to serve.
Preheat broiler on high setting. Brush the 1 tablespoon dressing over all sides of fish. Place fish on greased unheated rack of broiler pan. Broil about 4 inches from heat for 8 to 12 minutes or until fish flakes easily when tested with a fork, gently turning once halfway through broiling. (Or grill fish on the greased rack of uncovered grill directly over medium coals for 8 to 12 minutes, gently turning once halfway through grilling.) Slice fish.
Meanwhile, in covered medium saucepan cook potatoes in a large amount of boiling water for 7 minutes. Add green beans; cook about 2 minutes more or until potatoes are tender. Drain and cool slightly.
Arrange fish, potatoes, green beans, lettuce leaves, radishes, and olives on a platter. Sprinkle with red onion and black pepper. Serve with remaining dressing. Makes 4 servings.