Stir 1 (28-ounce) can diced tomatoes and their juices, 1 cup low-sodium chicken broth, 1 tablespoon chili powder, 1 tablespoon ground cumin, 2 teaspoons kosher salt, and 2 teaspoons ground cumin together in a 4-quart or larger slow cooker. Add 2 1/2 to 3 pounds boneless, skinless chicken in an even layer.
Cover and cook on the LOW setting until the chicken is cooked through, 5 to 6 hours.
Uncover and stir in 2 (about 15-ounce) cans drained and rinsed black beans and 2 cups frozen corn kernels. Cover and cook for 15 to 30 minutes more to warm the beans and corn through.
Use 2 forks to shred the chicken into bite-sized pieces directly in the slow cooker. Taste and season with more kosher salt as needed. Serve on top of cooked rice with the toppings of your choice.