Thaw fish, if frozen. Rinse fish; pat dry. For dressing, in a small bowl combine vinegar and shallots. Whisk in mustard. Add oil in a thin, steady stream, whisking constantly. Stir in the anchovy; season to taste with salt and black pepper. Remove 1 tablespoon of the dressing for brushing fish; set aside remaining dressing until ready to serve.

Brush the 1 tablespoon dressing over both sides of fish. Place fish on the greased, unheated rack of a broiler pan. Broil about 4 inches from the heat for 8 to 12 minutes or until fish flakes easily with a fork, gently turning once halfway through broiling. (Or grill fish on the greased rack of an uncovered grill directly over medium coals for 8 to 12 minutes, gently turning once halfway through grilling.) Cut fish into slices.

Meanwhile, in a medium saucepan cook potatoes in boiling water for 7 minutes. Add green beans; cook for 2 minutes more or until potatoes are tender. Drain and cool slightly.

To serve, arrange fish, potatoes, green beans, lettuce leaves, radishes, and, if desired, the olives on 4 dinner plates. Serve with the remaining dressing.