In a bowl, whisk together barbecue sauce, lime juice, and honey. Place chicken in a large bowl and pour half of the marinade over top. Toss to coat. Marinate for 1 to 4 hours in the fridge. Reserve remaining marinade.
Preheat barbecue to medium-high.
For each skewer: slide 1 onion wedge onto skewer to within 5 cm (2-in.) of base, followed by one chicken cube, one avocado cube, and another onion wedge. Repeat 3 times.
Place brochettes on well-oiled barbecue grill. Reduce heat to medium, close the lid, and grill for 8 to 10 minutes, turning brochettes twice and brushing regularly with reserved marinade.
Remove brochettes to a serving platter; sprinkle immediately with sesame seeds and cilantro