Preheat your grill or oven to 400°F (200°C).
- In a large bowl, toss the chicken strips with olive oil, fajita seasoning, garlic powder, onion powder, salt, and pepper until the chicken is evenly coated.
- Lay out 4 large pieces of aluminum foil. Evenly divide the cooked rice, chicken, bell peppers, and onions among the four pieces of foil.
- Fold the foil over the chicken and vegetables, creating sealed packets. Make sure the packets are tightly sealed to keep in the steam and juices while cooking.
- If grilling: Place the foil packets on the grill over medium heat and cook for 15-20 minutes, or until the chicken reaches an internal temperature of 165°F (75°C). If baking: Place the foil packets on a baking sheet and bake in the oven for 20-25 minutes.
- Carefully open the foil packets (watch out for steam!) and sprinkle with shredded cheddar cheese, if using. Close the foil packets again and cook for an additional 2-3 minutes until the cheese is melted.
- Serve the fajitas directly from the foil packets with lime wedges and cilantro, if desired.