Core the bell peppers and peel the red onion. Then cut the veggies into strips. Transfer to a large mixing bowl. Cut the chicken breasts into strips and add them to the bowl with the veggies.
Add the chili powder, cumin, garlic powder, onion powder, and salt to a small bowl. Stir until combined. Pour over the chicken and veggies. And then use your hand to toss until everything is well coated in the spice blend.
Lay out four large squares of foil on the counter. Divide the chicken and veggies evenly between the foil. Wrap the foil up by first folding the sides over the top so that they overlap, and then roll up the ends so nothing can fall out.
Cook on a preheated grill over indirect heat or in the oven at 400 degrees F for 20 - 25 minutes or until chicken is cooked through.
Carefully open the foil packets (there will be steam). Transfer the fajitas to a serving platter along with tortillas, or top with sour cream, cilantro, and serve with lime wedges right in the foil.