01 - In a medium bowl, whisk together the soy sauce, pineapple juice, brown sugar, olive oil, garlic, ginger, and black pepper until the sugar dissolves and the mixture is well blended.
02 - Place the chicken breasts in a large resealable plastic bag or shallow dish. Pour the marinade over the chicken, turning each piece to coat evenly. Seal the bag or cover the dish and refrigerate for at least 30 minutes, or up to 4 hours for deeper flavor penetration.
03 - Preheat an outdoor grill or grill pan to medium-high heat (approximately 400°F). Lightly oil the grill grates to prevent sticking.
04 - Remove the chicken from the marinade, allowing any excess to drip off. Discard the remaining marinade. Grill the chicken for 5 to 7 minutes per side, or until the internal temperature reaches 165°F when measured with a meat thermometer. Transfer to a plate and let rest for 5 minutes before serving.
05 - While the chicken rests, place the pineapple rings on the grill and cook for 2 to 3 minutes per side until nicely charred with visible grill marks.
06 - Arrange the grilled chicken on serving plates and top each breast with a grilled pineapple ring. Garnish with thinly sliced green onions and a sprinkle of sesame seeds if desired. Serve immediately.