Divide rice into 6 lunch containers. Set aside. Heat oil in a large skillet over med-high heat. Season chicken with salt and pepper, then stir fry until brown it and set aside on plate. In the hot skillet stir fry the carrots, broccoli, and onions until crisp-tender. Add garlic and stir fry until fragrant. Add chicken to the skillet with the vegetables. Add in two thirds of the stock, soy sauce, and brown sugar. Bring to boil. Stir together remaining stock with the corn starch. Set aside until liquid in pan is at a boil, then add the cornstarch mixture and stir constantly until thickened. Divide chicken and vegetable mixture into pint freezer bags over rice.