In a large bowl, mix together the hoisin, soy sauce, and 3 tablespoons of pineapple juice. Reserve 4-5 tablespoons of this mixture in a small covered bowl in the refrigerator for use later.
Season chicken with salt and pepper. Add the minced garlic and chicken to the marinade. Cover and refrigerate for at least 2 hours or up to overnight.
Slaw Topping
In a medium bowl, combine the rice vinegar, mayonnaise and 2 tablespoons of the reserved marinade. Add the coleslaw mix, green onion and cilantro. Toss to coat. Taste and adjust seasoning then refrigerate until ready to use. (You can do this up to 24 hours in advance).
Grilled Chicken
Heat a large grill pan or heavy skillet over medium-high heat. Add a drizzle of oil and cook the chicken, about 3-5 minutes per side, until a thermometer registers the internal temperature to 165℉. Transfer to a plate to rest. (Note - if the outside is becoming too dark, finish the chicken in a 375℉ oven until recommended temp is reached).
In the same pan, place 4 pineapple rings and cook on both sides for 1-2 minutes, until nicely browned and caramelized.
To build the sandwich, brush chicken with remaining reserved marinade and place on the bottom bun, top with a grilled pineapple ring and some slaw. Serve immediately.
Notes
Boneless, skinless chicken thighs can be used. Make sure to cook thoroughly to 170℉.You can use fresh cut pineapple in place of the canned rings. If using fresh pineapple, add 1.5 tablespoon of sugar in place of the pineapple juice the recipe calls for.