01 - Whisk together soy sauce, pineapple juice, olive oil, garlic powder, and black pepper in a bowl. Add chicken breasts and coat thoroughly. Marinate for at least 15 minutes, or up to 2 hours for deeper flavor penetration.
02 - Combine soy sauce, pineapple juice, brown sugar, and rice vinegar in a small saucepan. Bring to a simmer over medium heat, stirring until sugar dissolves. Add cornstarch slurry while stirring constantly. Cook for 1-2 minutes until sauce thickens to coating consistency. Remove from heat.
03 - Heat grill or grill pan to medium-high temperature, approximately 375-400°F.
04 - Remove chicken from marinade and discard excess liquid. Grill chicken for 5-6 minutes per side until internal temperature reaches 165°F and juices run clear. During final 2 minutes of cooking, place pineapple rings on grill until lightly caramelized with distinct char marks.
05 - Place burger buns cut-side down on grill for 30-60 seconds until golden brown and lightly crisp.
06 - Spread mayonnaise on bottom bun if desired. Layer lettuce leaf, grilled chicken breast, and drizzle with 1-2 tablespoons teriyaki sauce. Add grilled pineapple ring, tomato slice, and red onion. Top with remaining bun half.
07 - Serve immediately while chicken is warm and bun retains slight crunch from toasting.