Spray crockpot evenly with PAM. Add chicken breasts (they can be frozen or thawed). Pour chicken stock over chicken breasts and season with salt, pepper, and sage. Next, layer corn, mushrooms, and green beans. In a separate bowl, mix stuffing and mushroom soup together. Top chicken, corn, and beans with stuffing mixture. Set crockpot on high and cook 4-6 hours or low for 7 hours.