Place fish in a shallow dish. Combine green onions and next 5 ingredients; spoon half of green onion mixture over fish. Cover and chill at least 2 hours.
Combine remaining green onion mixture, succotash, and next 3 ingredients in a bowl. Cover and chill.
Place fish on a grill rack coated with cooking spray. Grill 5 minutes on each side or until fish flakes easily when tested with a fork. Serve with succotash mixture.
Note: If frozen succotash is not available in your area, substitute 1 cup each of frozen baby lima beans and whole-kernel corn.