Coat a large nonstick skillet with cooking spray, add oil and place over medium-high heat until hot. Add green onions and carrot; cook 3 minutes or until vegetables are tender, stirring often.
Combine vinegar, sugar, and soy sauce in a small bowl, stirring until sugar dissolves. Add to carrot mixture; bring just to a boil. Add fish; cover, reduce heat, and simmer 10 minutes or until fish flakes easily when tested with a fork. Transfer fish to a serving platter; set aside and keep warm.
Combine orange juice and cornstarch in a small bowl, stirring until smooth. Add to liquid in skillet. Bring to a boil, and cook, stirring constantly, 2 minutes or until sauce is slightly thickened. Spoon sweet-and-sour sauce evenly over fish.