To prepare the vinaigrette, combine first 6 ingredients in a small bowl; stir with a whisk.
To prepare fish, heat a nonstick grill pan over medium-high heat. Coat pan with cooking spray. Sprinkle fish with 1/2 teaspoon salt. Add fish to pan; grill 4 minutes on each side or until fish flakes easily when tested with a fork or until desired degree of doneness. Spoon vinaigrette over fish. Sprinkle with chives.