In a small bowl, blend cornstarch with soy sauce until smooth. Add sherry, sugar and ginger. Combine this sauce and meat; marinate for one hour. Strain marinade from meat and reserve marinade. In wok or large heavy skillet, heat olive oil and salt until very hot. Add meat and brown on both sides. Add garlic and mushrooms; stir fry for two minutes. Add marinade and heat through. (If necessary, thicken with a small amount of cornstarch diluted in water.) Delicious served over rice. 4 Servings.