Place the 4 chicken breasts in the bottom of the slow cooker in a single layer.
Sprinkle the chicken evenly with 2 tablespoons taco seasoning.
Add the chopped green bell pepper, drained canned corn, rinsed and drained black beans, and 1½–2 cups salsa on top of the chicken.
Cover and cook on HIGH for 3½–4 hours, or until the chicken is cooked through and reaches 165°F (74°C).
Remove the chicken to a cutting board and shred with two forks or pull apart with tongs.
Return the shredded chicken to the slow cooker and stir to combine with the juices and vegetables.
Serve the shredded Tex‑Mex chicken over cooked rice and top with chopped cilantro, green onions, sour cream, shredded cheese, and diced tomatoes as desired.