HEAT THE OIL IN A WOK or large skillet over high heat. Reduce the heat to medium high, add the chicken cubes and mushrooms and stir-fry, stirring constantly, for 3 minutes. Add the garlic, salt and pepper to the pan, and continue to stir-fry for 3 minutes more, stirring constantly, or until the chicken cubes are cooked through. Add the butter, parsley and chicken stock to the pan, stir-fry for 1 minute, and serve immediately.