Place chicken breasts in the slow-cooker and cover with the broth, salsa, corn, beans and taco seasoning.
Cover and cook on LOW for 4-6 hours.
Remove the chicken and either shred it or cut it up into bite-size pieces.
Stir in the sour cream.
In a small bowl, combine the cornstarch and water; stir until smooth. Stir cornstarch mixture into the slow-cooker mixture.
Put the chicken back into the slow-cooker.
Keep lid off; turn to HIGH and let the mixture thicken for about 30 minutes.
Spoon the chicken mixture over tortillas and sprinkle with cheese and diced tomatoes.
