If scallops are large, cut in half and set aside. In a small bowl, combine the cornstarch, sugar and salt. Stir in water and soy sauce until smooth; set aside.
In a nonstick skillet, saute carrots and celery in 1-1/2 teaspoons hot oil for 4 minutes. Add mushrooms and green onions; stir-fry for 2-3 minutes or until crisp-tender. Add the garlic, curry powder and ginger; stir-fry for 1 minute longer. Remove vegetable mixture and set aside.
In the same skillet, stir-fry scallops in remaining oil for 2-3 minutes or until scallops turn opaque. Stir sauce and add to the pan. Bring to a boil; cook and stir for 1-2 minutes or until thickened. Return vegetables to the pan; heat through. serve over hot cooked rice if desired.