Lay out four large foil squares (about 10x10 inches) and spray with cooking spray. Place a chicken breast in the center of each piece and season with chili powder, salt, and pepper.
Top each chicken breast with black beans, corn, diced bell peppers, and salsa. Make sure the veggies are evenly spread for consistent cooking.
Fold the foil ends to create sealed packets. Grill packets over medium-high heat for 10 minutes, then flip and cook for another 10–12 minutes until chicken reaches 165°F.
Open the packets carefully and sprinkle with cheese. Return packets to the grill or oven for 2–3 minutes until the cheese melts. Top with cilantro, guacamole, or sour cream before serving.