Cut chicken in medium size pieces. Combine salt, pepper, 1 tablespoon soy sauce and 1/3 cup pineapple syrup and marinate chicken in this mixture for 1 hour.Combine rest of syrup with ketchup, half of garlic, rest of soy sauce, sugar and chicken stock.
Dredge chicken in arrowroot and stir to coat pieces well. Heat oil in a skillet and fry chicken pieces until lightly browned. Place chicken pieces in paper towel to eliminate excess fat.
Heat 2 tablespoons oil in a large pan. Add remaining garlic and sauté for 1 minute. Stir in white part of onion and pepper. Add the pineapple syrup and chicken stock mixture. Bring to a boil for a few minutes and add fried chicken. Lower heat and cook 10 minutes, approximately. Add diced pineapple. If a thicker sauce is desired, dilute 1 tablespoon arrowroot in ¼ cup cold water and stir into mixture while boiling.Add green part of onion, before serving.Place in a serving dish and decorate with slices of pineapple. Serve with white rice.