Drain the pineapple, reserving 1 cup of the pineapple juice. Save the pineapple slices for later use
Place the pineapple juice, soy sauce, brown sugar, ketchup and sesame oil in a large bowl. Whisk to combine.
Reserve 2 tablespoons of the marinade in the refrigerator in a small bowl. This will be used later on to baste the chicken.
Stir the garlic and ginger into the large bowl of marinade. Add the chicken thighs and toss to coat.
Cover the bowl and refrigerate for at least one hour, or up to 24 hours.
Preheat an outdoor grill or grill pan to medium heat.
Remove the chicken from the marinade and place on the grill. Cook for 6-8 minutes per side or until chicken is done, basting occasionally with the reserved marinade.
Place the pineapple slices on the grill. Cook for 2 minutes per side.
Place the pineapple and chicken on a plate. Sprinkle with green onions, then serve.
