Place 1 1/2 cups salsa, the 1-oz package of taco seasoning, and the chicken breasts into the slow cooker and stir to coat.
Cover and cook on LOW for 6 to 8 hours, or until the chicken is cooked through and tender.
Remove the chicken to a cutting board and shred with two forks; return shredded chicken to the slow cooker.
Add 1 cup frozen corn and the drained, rinsed 15-oz can of black beans to the slow cooker, stir to combine, then cover and cook on LOW for an additional 15 minutes to heat through.
Stir, taste, and adjust seasoning if needed, then serve in tortillas with desired toppings.