Drain the juice from your pineapple chunks into your work bowl.
Reserve chunks in a sealed plastic baggie until ready to use.
Add your soy sauce, brown sugar, garlic, onion, ginger and coconut milk to the bowl of juice. Whisk to combine.
Pour marinade into a large baggie and add chicken pieces.
Seal and store in the refrigerator for 8 to 24 hours. When ready to cook, remove from marinade, discard marinade and preheat grill to high heat.
Skewer pineapples on their own skewers. Cook time on pineapples is just until charred a bit (about 5 minutes).
Cook time on your chicken will vary by size of your chunks. Grill until cooked through (most likley 9-11 minutes) turning once. Due to the marinade, your chicken will char a bit. Once it gets a nice char via direct heat you might want to then finish cooking via indirect heat to allow chicken to cook through but not burn on the outside (the brown sugar may cause it to char and if you choose to do whole pieces with skin...it definitely will).
Serve on a platter alone with the pineapples or over rice.
*If you are using fresh pineapple, you need about a cup of pineapple juice for the marinade.
Don't pack skewers too tightly or cook time will be longer.
The coconut milk really lends something great to this dish, don't skip it. If the milk is solidified at the top of the can, scrape that part into a small bowl and microwave just until melted. Allow it to cool to room temperature before you add it to the marinade.