Place the chicken breasts in the bottom of the slow cooker.
Sprinkle the chicken evenly with the chili powder, ground cumin, crushed red pepper, sea salt, and cracked black pepper.
Add the diced green chile or jalapeño, diced red onion, minced garlic, diced tomatoes (with liquid), black beans, and corn on top of the seasoned chicken; gently stir to distribute ingredients.
Cover and cook on low for 4–6 hours, or until the thickest part of the chicken reaches 165°F (about 360 minutes total cook time).
Remove the chicken to a cutting board and shred with two forks, or shred directly in the slow cooker with forks; return shredded chicken to the cooker and stir to combine.
Keep the slow cooker on warm until ready to serve.
Assemble bowls by dividing cooked rice among bowls and topping with the chicken mixture, diced roma tomato, avocado, shredded cheese, romaine lettuce, cilantro, and lime wedges as desired.