In a gallon size zip-top freezer bag or in between two layers of plastic wrap, pound the chicken to about 3/4-inch thickness, with either a meat tenderizer or a wooden rolling pin.
Whisk together the chicken marinade ingredients in a large glass measuring cup. Reserve 1/3 cup in the refrigerator for making your glaze.
In another gallon size zip-top freezer bag, pour marinade and squish around with your hand, from the outside of the bag. Place the flattened chicken breasts into marinade. Seal the bag, and massage the chicken with your fingers to coat in the marinade. Place the entire bag onto a baking sheet or pan, position so it sits flat. Let marinate in the refrigerator for 4 hours or up to 24 hours.
Preheat the outdoor grill to medium high heat. Scrape any debris from the grill grates.
Cook on the grill, over direct heat, close the grill, and cook for about 6 minutes. Use tongs to flip the chicken, close the grill, and cook for an additional 6 minutes. Or until the chicken has an internal temperature of 165 degrees F. Transfer the cooked chicken to a half sheet pan lined with clean parchment paper or clean serving plate. Cover with aluminum foil to keep warm. Let rest for 5 minutes before slicing.
As the chicken cooks, grill the pineapple slices. Cook until you have good grill marks on both sides of the pineapple slices, about 3 minutes each side.
Bring the reserved marinade to a boil in a small saucepan. Whisk in 1 teaspoon corn starch dissolved in a few tablespoons of cold water. Whisk continuously until thickened slightly. Remove from the heat and brush on the chicken.