Combine first 3 ingredients, and rub evenly over pork.
Heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add pork to pan, and cook 1 1/2 minutes on each side or until lightly browned. Remove pork from pan, and set aside.
Reduce heat to medium. Add 2 tablespoons onions, ginger, and garlic to pan; cook 2 minutes or until fragrant, stirring constantly. Combine sherry and next 5 ingredients (through soy sauce) in a small bowl. Add sherry mixture to pan; bring to a boil, scraping pan to loosen browned bits. Add pork to pan; cook 3 minutes or until pork is done. Remove pork from pan using a slotted spoon, reserving liquid in pan.
Combine water and cornstarch in a small bowl, stirring with a whisk. Add cornstarch mixture to pan, and bring to a boil. Cook 30 seconds or until slightly thickened. Serve over pork. Sprinkle with 1/4 cup green onions.