01 - Whisk together soy sauce, pineapple juice, olive oil, garlic powder, and black pepper in a shallow dish. Add chicken breasts and turn to coat evenly. Let marinate at room temperature for 15 minutes or refrigerate up to 2 hours.
02 - Combine soy sauce, pineapple juice, brown sugar, and rice vinegar in a small saucepan over medium heat. Bring to a gentle simmer. Whisk in cornstarch slurry and cook for 1-2 minutes, stirring constantly, until sauce thickens and coats the back of a spoon. Remove from heat and set aside.
03 - Preheat grill or grill pan to medium-high temperature (375-400°F). Lightly oil the grates to prevent sticking.
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, place pineapple rings on the grill and cook until lightly charred with caramelized grill marks.
05 - Place hamburger buns cut-side down on the grill for 30-60 seconds until lightly toasted and golden brown.
06 - Spread mayonnaise on toasted bottom buns. Layer lettuce leaves, grilled chicken breasts, and drizzle generously with teriyaki sauce. Add grilled pineapple rings, tomato slices, and red onion. Top with remaining bun halves and serve immediately.