In a mixing bowl whisk together ketchup, brown sugar, soy sauce, pineapple juice, 2 Tbsp olive oil, rice vinegar, garlic, ginger and sesame oil. Stir in 3/4 tsp pepper and season with salt if desired. Place chicken in a gallon size resealable bag. Reserve 1/2 cup of the marinade in refrigerator then pour remaining marinade over chicken. Seal bag and refrigerate 1 – 2 hours (meanwhile soak 10 wooden skewer sticks in water for 1 hour).