In a large bowl or jug, combine all of the marinade ingredients (pineapple juice, ketchup, brown sugar, soy sauce, rice vinegar, sesame oil, sriracha, garlic, and ginger).
Give the marinade a whisk then pour HALF of it over the chicken thighs, and mix so the chicken thighs are thoroughly coated. Cover, and allow to marinate in the fridge for at least 30 minutes but preferably longer, and up to 24 hours. Alternatively, this can be done in a ziptop bag.
Peheat the grill to medium high heat, then clean and oil the grill grates.
Remove the chicken from the marinade, and place on the grill and cook for 3 minutes, then flip and cook for 2 more minutes.
Baste with the reserved marinade with a brush, cook for a minute, then flip and baste again. Repeat 2 more times. Grill until the until the chicken is cooked through, and reaches an internal temperature of 165°F/74°C.
Allow to rest for 5 minutes before slicing, and garnish with green onions if desired. Serve with grilled pineapple, or pineapple salsa on the side, and fresh lime wedges.