1/2 c. soy sauce
1/4 c. white wine or lemon juice
1/4 c. oil
1/4 c. chopped onion
1/4 tsp. fresh minced garlic

Mix all ingredients and pour over boneless chicken breasts. Marinate for at least 30 minutes, but preferably 2 hours. Grill on medium heat for about 4 minutes on each side or until done.

Note: I usually pound the breasts slightly to have a consistent thickness for even cooking.