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. Marinate for 15 minutes at room temperature or refrigerate 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. Whisk in cornstarch slurry and cook 1-2 minutes until sauce thickens. Remove from heat.
03 - Preheat grill or grill pan to medium-high heat (about 400°F). Lightly oil the grates to prevent sticking.
04 - Remove chicken from marinade and discard excess liquid. Grill chicken 5-6 minutes per side until internal temperature reaches 165°F. During final 2 minutes, add pineapple rings to grill until caramelized and marked.
05 - Place burger buns cut-side down on the grill for 30-60 seconds until lightly toasted and golden.
06 - Spread mayonnaise on bottom bun if desired. Layer lettuce, grilled chicken, teriyaki sauce, grilled pineapple, tomato slices, and red onion. Top with upper bun and serve immediately.