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, or refrigerate for up to 2 hours for deeper flavor.
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 and cook for 1-2 minutes, stirring constantly until sauce thickens. Remove from heat and set aside.
03 - Heat grill or grill pan to medium-high temperature (about 375°F to 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. During the final 2 minutes of cooking, place pineapple rings on the grill and cook until lightly caramelized with grill marks.
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, grilled chicken breast, teriyaki sauce, grilled pineapple ring, tomato slice, and red onion. Top with upper bun and serve immediately.