Drain pineapple rings and reserve the juice. Set pineapple aside.
20 ounce can pineapple rings
In a large bowl whisk together pineapple juice, ketchup, soy sauce, brown sugar, vinegar, ginger, garlic, and sesame oil until combined.
1/3 cup ketchup, 1/2 cup soy sauce, 1/2 cup brown sugar, 2 Tablespoons cider vinegar, 3 teaspoons minced ginger, 3 teaspoons minced garlic, 1 Tablespoon sesame oil
Reserve 1 cup of the marinade for later use.
Add chicken to the remaining marinade, toss to coat, cover, and refrigerate for at least 3 hours or overnight, turning occasionally.
3 pounds chicken thighs
Preheat grill to medium heat and oil grates well.
Remove chicken from marinade and discard used marinade.
Place chicken on grill, cover, and cook for 25–30 minutes, turning frequently and basting with reserved marinade. Spray pineapple rings lightly with cooking spray and grill for 2 minutes per side until lightly charred.
Cook chicken until internal temperature reaches 165° F.
Top with scallions and serve with grilled pineapple.