Preheat oven to 425°F. Line a large rimmed baking sheet with aluminum foil or parchment paper.
In a small bowl, whisk together soy sauce, pineapple juice, brown sugar, rice vinegar, minced garlic, grated ginger, and cornstarch until smooth.
Place chicken pieces, bell peppers, red onion, and pineapple chunks on the prepared sheet pan. Drizzle with olive oil and season with salt and pepper.
Pour about two-thirds of the sauce over everything and toss gently to coat evenly. Spread into a single layer with space between pieces.
Bake for 20 to 25 minutes, stirring once halfway through. Chicken should reach an internal temperature of 165°F.
Garnish with sesame seeds and green onions before serving. Serve over rice if desired.