In a bowl, whisk together pineapple juice, soy sauce, brown sugar, ketchup, rice vinegar, garlic, ginger, sesame oil, and black pepper until fully combined.
Place chicken in a resealable plastic bag or shallow dish and pour half the marinade over it. Reserve the other half for basting later.
Seal and refrigerate the chicken for at least 1 hour or ideally overnight.
Preheat grill to medium-high heat. Remove chicken from marinade and discard used liquid.
Grill chicken for 6–7 minutes per side, basting with the reserved marinade as it cooks. Internal temperature should reach 165°F (75°C).
Rest chicken for 3–5 minutes, then slice and serve over rice. Garnish with chopped green onions and add grilled pineapple slices if desired.