In a medium bowl, whisk together soy sauce, pineapple juice, ketchup, dark brown sugar, olive oil, sesame oil, minced garlic, minced ginger, salt, and black pepper until smooth.

Cut boneless chicken breasts into bite-sized pieces and marinate in half of the marinade in the refrigerator for at least 1 hour, preferably overnight.

Chop bell peppers and red onion into uniform pieces while soaking wooden skewers in water for 30 minutes to prevent burning.

Thread chicken, pineapple chunks, bell pepper pieces, and red onion alternately onto skewers.

Preheat grill to medium-high heat, about 375°F to 425°F, brushing grates with olive oil.

Grill skewers for 10-12 minutes, turning occasionally, until chicken is cooked through and pineapple is caramelized.

In a saucepan, bring remaining marinade to a boil, adding cornstarch mixed with water to thicken for dipping sauce.