Sweet-Sour Sauce

Combine sugar, vinegar, ketchup, chicken broth, soy sauce, and cornstarch in small bowl; stir well to combine.

Heat vegetable oil in wok or heavy medium skillet over high heat until rippling. Add scallions, garlic, and ginger; stir-fry until fragrant, about 30 seconds. Reduce heat to medium; add sweet-sour mixture. Stir-fry until all ingredients are well combined and sauce has thickened, about 30 seconds. Stir in sesame oil; remove from heat.