Soak 6 bamboo skewers in water for a minimum of 30 minutes.

In a small saucepan, combine the soy sauce, pineapple juice, brown sugar, rice vinegar, sesame oil, ginger, garlic, and red pepper flakes and bring to a boil over medium-high heat. Reduce the heat to medium-low and simmer for 5 minutes.

Meanwhile, in a small bowl combine the water and cornstarch. Whisk the mixture into the simmering soy sauce mixture and let it thicken. Remove from heat and set aside to cool.

Once the sauce has cooled completely, place the cubed chicken in a large resealable plastic bag (you can also use a covered shallow dish). Add half the teriyaki sauce (save the rest for later) and gently turn the bag over to coat the chicken. Marinate in the refrigerator for 1 hour minimum (or overnight)

Alternate pieces of marinated chicken, red bell pepper, green bell pepper, red onion, and pineapple on the prepared skewers until the ingredients have all been used.

Preheat a grill to medium heat (350-400 degrees F). Once hot, oil the grates thoroughly. Add the skewers, cover the grill, and cook, turning every 3-4 minutes, until the chicken has reached an internal temperature of 165 degrees F (15-20 minutes). After 2 turns, begin basting the chicken with the remaining teriyaki sauce after each turn. If the chicken starts charring too quickly while basting, you can lower the heat as needed. Serve hot.