Arrange tomatoes, onion, and half of the salsa in the bottom of a slow cooker.
Place chicken on top, sprinkle with the taco seasoning, and pour the remaining salsa over all.
Cover and cook until the chicken reaches an internal temperature of 165°F, about 2-4 hours on LOW or about 1-2 hours on HIGH.
Remove the chicken to a cutting board. Add the cream cheese to the slow cooker and stir. Cover and continue cooking until the cream cheese melts, about 5-10 more minutes. Stir again to make sure that the cream cheese is smoothly incorporated into the sauce.
While the cream cheese is in the slow cooker, use two forks to shred the chicken. Stir the shredded chicken back into the sauce and cook for a few more minutes, until warmed through.
