In a large bowl, combine the olive oil, lemon juice, minced garlic, and salt and pepper. Add the chicken pieces, making sure they are well-coated with the marinade. Cover and refrigerate for at least 1 hour, up to overnight.
If you're using wooden skewers, soak them in water for 30 minutes prior to grilling to prevent burning.
Preheat your grill to medium-high heat.
Thread the marinated chicken pieces onto the skewers, alternating with pieces of bell pepper, onion, and your chosen fruit (if using).
Place the skewers on the grill. Cook for 5-7 minutes per side, or until the chicken is no longer pink in the middle and the vegetables are slightly charred.
Remove the skewers from the grill and let them rest for a few minutes before serving.