1. Prepare grill.
2. Combine cucumber and next 4 ingredients in a small bowl. Stir in 1/8 teaspoon salt and 1/4 teaspoon pepper. Cover and chill until ready to use.
3. Sprinkle fish evenly with 1/4 teaspoon salt and 1/4 teaspoon pepper.
4. Place fish on grill rack coated with cooking spray. Grill 4 to 5 minutes on each side or until fish flakes easily when tested with a fork. Serve with sour cream mixture.