Combine seasoning mix in a small bowl. Sprinkle chicken with 2 teaspoons of seasoning mix. Dissolve cornstarch in 1/4 cup apple juice and set aside. Preheat a skillet over high heat for 4 minutes. Lower heat and Place chicken in skillet and brown on both sides about 4 minutes per side. Return the heat to high ans tir in 1/2 cup of stock. Add onions and the remaining seasoning mix, stir and cook until all the liquid evaporates, about 4 minutes. Stir in 1/4 cup of lemon juice. Cook until liquid evaporates about 4 minutes. Add 1/2 cup of the apple juice and cook until about half the liquid evaporates, about 3 minutes. Stir in the remaining 1 cup of stock, the 1/4 cup lemon juice and the 1/2 cup apple juice. Bring to a boil, whisk in the cornstarch/apple juice mixture and return to a boil. Return the chicken to the skillet, lower the heat to medium and cook until the chicken is done all the way through about 5 minutes. Turn off the heat, remove the chicken and whisk in the sweetener.