In a large bowl whisk together ketchup, brown sugar, soy sauce, pineapple juice, 2 Tbsp olive oil, rice vinegar, garlic, ginger, sesame oil, salt and pepper. Separate 1/2 cup into another bowl and refrigerate for later use.
Place chicken in a gallon size resealable bag and pour remaining marinade over chicken. Seal bag, turn and knead to coat chicken, then refrigerate for 1 hour. If you are using wooden skewers, soak in water for the hour while the chicken is marinating.
Meanwhile, place onion, bell pepper and pineapple in a large bowl, drizzle with remaining olive oil and toss to coat. Season with salt and pepper, then thread onion, bell pepper, pineapple and chicken onto skewers until all of the chicken has been used.
Preheat grill over medium heat to 400°F. Brush grill grates with olive oil then place skewers on grill. Grill 5 minutes then brush along tops with 1/2 of the marinade you set aside earlier. Flip skewers and brush with remaining marinade. Cook for 4-5 more minutes, or until chicken reads 165°F in center on an instant read thermometer. Serve warm with rice or your favorite sides!