In A Skillet Over Medium Heat, Saute Garlic And Onions In Butter And Oil Until Onions Are Tender. Add Chicken, Salt If Desired And Pepper. Cook For 6-8 Minutes Or Until Chicken Juices Run Clear. Add Tomatoes, Lemon Juice And Sugar; Heat Through. Combine Cornstarch And Water; Stir Into Chicken Mixture. Bring To A Boil; Cook And Stir For 1 Minute Or Until Thickened. Add Parsley. Serve Over Rice If Desired.