Make the Marinade:
In a medium bowl, whisk together pineapple juice, soy sauce, honey, olive oil, garlic, ginger, and chili flakes.
Marinate the Chicken:
Place the chicken in a resealable plastic bag or bowl. Pour the marinade over it and refrigerate for at least 1 hour or up to 8 hours for best flavor.
Preheat the Grill:
Heat your grill to medium-high. Lightly oil the grates to prevent sticking.
Grill the Chicken:
Remove chicken from the marinade, letting excess drip off. Grill for 5–6 minutes per side until cooked through (internal temp 165°F / 74°C).
Grill the Pineapple:
Add pineapple slices to the grill and cook 2–3 minutes per side until golden and caramelized.
Serve:
Place grilled chicken on a plate, top with pineapple slices, and drizzle with any thickened leftover sauce. Serve warm.