Preheat oven to 350°F (175°C). Lightly spray a rimmed 18x13-inch baking sheet with non-stick cooking spray.
In a medium mixing bowl, whisk together soy sauce, ketchup, pineapple juice concentrate, brown sugar, rice vinegar, cornstarch, Worcestershire sauce, garlic, ginger, and black pepper until smooth.
Spread diced chicken, bell peppers, and red onion evenly on the prepared sheet pan.
Pour the sauce over the chicken and vegetables. Toss everything to coat evenly.
Bake in preheated oven for 10 minutes.
Remove from oven, toss the mixture, and sprinkle fresh pineapple cubes over the top.
Return to oven and bake for an additional 7-10 minutes, or until chicken reaches an internal temperature of 165°F.
Toss everything once more to coat in the sauce before serving.
Garnish with chopped cilantro if desired. Serve warm over coconut rice, white rice, or brown rice.