1. Preheat grill to medium-high heat and prepare four large rectangular pieces of heavy-duty foil. Spray each piece with nonstick cooking spray or lightly oil to prevent sticking.
2. Season each chicken breast on both sides with chili powder, salt, and pepper (or taco seasoning if using). Place one breast in the center of each foil piece.
3. In a bowl, mix black beans, corn, bell peppers, and salsa along with any remaining seasoning or lime juice/zest if desired. Spoon this mixture evenly over the chicken breasts.
4. Fold the foil over the chicken and vegetables, sealing edges tightly to form packets. Ensure packets are well sealed to trap steam.
5. Place packets on the grill and cook for about 10 to 12 minutes. Flip packets and continue grilling for another 10 to 12 minutes, or until the chicken reaches an internal temperature of 165°F. Rotate packets halfway through cooking for even heat distribution.
6. Carefully open the foil packets, sprinkle shredded cheese over the chicken and vegetable mixture, then reseal the packets just enough to hold in heat. Return to the grill for 2 to 3 minutes or until the cheese melts.
7. Remove packets from grill, open fully, and add optional toppings such as fresh cilantro, jalapeños, sour cream, sliced avocado, green onions, or a squeeze of lime. Serve the foil packets over warmed corn or flour tortillas, or with cooked rice if desired.