Mix cornstarch and ginger; then blend in soy, sherry, and broth and set aside. Place wok over high heat and add oil. When oil is hot, add garlic and shrimp and stir-fry for about 1 minute. Add peas and stir-fry for about 2 minutes (30 seconds if frozen). Add green onions, stir to mix. Add cornstarch mixture and stir until it boils and thickens.