Heat the coconut oil in a small sauce pan. Add the onion and sauté on medium heat for 2-3 minutes, or until it becomes translucent and soft. Add the garlic and sauté for another 30 seconds. Add the dates, orange juice concentrate, coconut aminos, honey, vinegar, salt, and chili flakes(if using) to the sauce pan and bring to a boil. Reduce the heat and simmer for 5 minutes. Mixture should have started to thicken a bit and dates should be soft.
Pour the mixture into a blender and puree until very smooth and thick.
Place the cubed chicken in a container or Ziploc bag and pour ¾ of the teriyaki sauce over it. Seal and let marinate in the refrigerator overnight, or for at least 30 minutes. Marinate overnight for best flavor. Reserve the rest of the teriyaki sauce in an airtight container and refrigerate.
When ready to make the skewers, thread the marinated chicken and pineapple cubes onto the soaked wooden skewers, alternating each item. You should end up with 8-10 skewers, depending on how heavily you thread them.
Preheat a grill, making sure to oil the grates before doing so.
Grill the skewers on all sides until cooked through, basting with the reserved teriyaki sauce while they cook.