Chop your chicken breasts into small pieces, about 1 to 1-½” thick, bite size.
Chop your bell pepper and onion into similar size pieces, about 1 to 1-½” wide.
Transfer the cubed chicken into a mixing bowl and add the mayonnaise and fajita seasoning. Mix until well-coated.
Add the marinated chicken and chopped vegetables to the skewers.
Place the skewers on the grill's grates and cook for 5-7 minutes per side until the chicken reaches an internal temperature of 165°F and the vegetables are soft.
Remove from the grill and serve immediately.
Notes
If using wooden skewers, soak them in water for 30 minutes prior to cooking.