Heat the oil in a wok or large skillet over medium-high heat. Cook the chicken until no longer pink in the center and the juices run clear, 7 to 10 minutes.
Place the green bell pepper, yellow bell pepper, red bell pepper, mushrooms, onion, teriyaki sauce, pineapple chunks with the juice, garlic powder, and crushed red pepper into the wok, and turn the heat to medium. Bring to a simmer, stir in the flour, and continue simmering 15 minutes until thickened.
