Combine olive oil, honey, minced garlic, thyme, smoked paprika, cayenne pepper (if using), salt, and pepper in a large mixing bowl. Whisk thoroughly until the honey is fully incorporated.
Add chicken cubes to the marinade, tossing gently to coat each piece evenly. Cover and refrigerate for at least 15 minutes, though 2 hours will deliver more flavor.
While the chicken marinates, soak wooden skewers in water to prevent burning. Thread the marinated chicken pieces, nectarine chunks, red onion, and bell pepper alternately onto the skewers, leaving small gaps between pieces.
Preheat your grill to medium-high heat (approximately 375-400°F). Place skewers on the grill and cook for 4-6 minutes per side, rotating occasionally for even browning. The chicken should reach an internal temperature of 165°F.
Remove skewers from the grill and let them rest for 2-3 minutes. This allows the chicken juices to redistribute throughout the meat. Serve immediately.