Combine first 7 ingredients in a 10-inch skillet. Bring to a boil; cover, reduce heat, and simmer 10 minutes. Add salmon, leave uncovered, and simmer 17 minutes or until fish flakes easily when tested with a fork. Remove fish from pan with a slotted spoon. (Salmon may be chilled, if desired.)
Arrange peas in a vegetable steamer. Steam, covered, 3 minutes or until peas are crisp-tender. Drain and plunge peas into ice water; drain. Set aside.
Arrange 2 cups lettuce, 1/4 cup watercress, 1/4 cup peas, and about 2 tablespoons radishes on individual serving plates; top with salmon. Spoon about 3 tablespoons Cucumber Dressing evenly over each serving.