Combine meat with 1/2 cup soy sauce, sugar, salt, pepper, ginger and garlic; mix until well blended.
Shape into 12 large, thin patties.
Combine bean sprouts, water chestnuts and onions.
Spread 2 to 3 tbs of this mixture over 6 patties.
Cover with the other 6 patties; pinch edges together.
Brush with remaining soy sauce.
Broil 3 to 4 minutes on each side, 4 inches from the flame, basting with soy sauce during cooking.