Place onion in the bottom of a greased slow cooker. Layer half of the chicken breasts on top of onions. Dust with half of the Jalapeño Popper Warm Dip Mix. Top with remaining chicken, then remaining mix. Cover; cook on low 4-6 hours. When chicken is cooked through, use two forks to shred. Add green chilies; stir to evenly incorporate chilies, onions and remaining juice. Use shredded chicken on sandwiches or in tacos.