Place the chicken breast side down on a cutting mat, with the drumsticks pointing towards you. Using sharp poultry shears, cut down one side of the backbone from tail to neck, then repeat on the other side. Completely remove and discard the backbone. Flip the chicken over, breast side up, and press down firmly on the breastbone to flatten.
Marinade
Mix the pineapple juice, soy sauce/coconut aminos, brown sugar/honey, ginger, garlic, Chinese five spice, fish sauce, and chili-garlic paste together in a large zipper-top bag.
Place the chicken inside the bag and squish around the chicken to evenly coat with the marinade. Allow the chicken to marinade in the refrigerator for 2 hours to overnight.
Remove the chicken from the refrigerator 1 hour before cooking to bring up to room temperature.
For a 3-burner gas grill, light the right and left burners set at medium-high heat. Close the lid and allow the grill to heat up for at least 10 minutes. Oil the grates and the chicken skin-side down in the center (where the burner is off).
Close the cover and cook for 45 to 50 minutes, until the juices between the leg and the thigh run clear or an instant-read thermometer reads 165F degrees. Carefully flip the chicken skin-side down over the hot side of the grill. Cook for 5 minutes, until the skin is charred and crisp.
Remove from grill and transfer to a large cutting board, skin-side up. Allow to rest 10 minutes before slicing and serving.
Core and slice fresh pineapple into rings, then cut them in half. Brush with olive oil and grill until charred, about 2 minutes per side. Transfer to a serving bowl or platter.
Serving Sauce
Pour the marinade into a medium saucepan. Bring to a boil then reduce heat and simmer for 10 to 15 minutes, or until reduced by half.
Notes
For a larger grill, use half of the burners and cook the chicken on the cool side.
For a charcoal grill - spread the lit charcoal evenly over one side. Cover grill and heat for 10 minutes. Oil grates and lay chicken skin-side down on the cool side (where there is no charcoal). Flip and char the chicken over the hot side for 5 minutes.
I do not recommend canned pineapple slices, they are too soft and will break apart on the grill....but I will not stop you from trying if that is the only pineapple available.
If you have small children or family members that do not like any spice that tingles their tongue, cut the chili-garlic paste down to 0.5 tablespoon. It is not overpowering, but it is noticeable.