01 - Whisk together soy sauce, pineapple juice, olive oil, garlic powder, and black pepper in a bowl. Add chicken breasts, turning to coat evenly. Let marinate for at least 15 minutes, 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 nicely. Remove from heat and set aside.
03 - Heat grill or grill pan to medium-high temperature, about 375-400°F.
04 - Remove chicken from marinade and place on preheated grill. Cook for 5-6 minutes per side until internal temperature reaches 165°F and juices run clear. During the final 2 minutes of cooking, add pineapple rings to the grill and cook until lightly charred and caramelized.
05 - Place burger buns cut-side down on the grill for 30-60 seconds until lightly toasted and golden brown.
06 - Spread mayonnaise on bottom bun if desired. Layer lettuce leaf, grilled chicken breast, and drizzle generously with teriyaki sauce. Add grilled pineapple ring, tomato slice, and red onion. Cap with top bun and serve immediately while warm.