Prepare the marinade by whisking together honey, minced garlic, soy sauce, olive oil, apple cider vinegar, smoked paprika, black pepper, and red pepper flakes (if using) in a medium bowl. Set aside.

Cut chicken into even 1.5-inch cubes. Cut bell peppers into chunks roughly the same size as the chicken pieces, slice the red onion into wedges, and clean mushrooms trimming stems.

Place chicken cubes in the bowl with marinade. Toss well to coat all pieces evenly. Cover and refrigerate for at least 20 minutes, up to 2 hours.

Preheat grill or grill pan to medium-high heat (about 400°F). If using wooden skewers, soak them in water for 30 minutes beforehand.

Thread marinated chicken and vegetables alternately onto skewers, leaving small gaps between pieces for even heat circulation.

Grill kabobs for 12-15 minutes, turning every 3-4 minutes for even cooking and char. Ensure chicken reaches an internal temperature of 165°F. Move kabobs to cooler parts of the grill if flare-ups occur.

Remove kabobs from grill and let rest for 5 minutes before serving.