Drain the pineapple through a fine mesh sieve and save the juice. Whisk the Teriyaki Sauce ingredients together in a small bowl. Remove ¼ cup and add it to medium bowl or resealable bag with the chopped chicken. Marinate at room temperature while you prep the rest of the ingredients or up to 30 minutes at room temperature (refrigerate if marinating longer, up to 4 hours then bring to room temperature before cooking). Set the remaining teriyaki sauce aside. Heat a drizzle of vegetable oil in a large nonstick skillet over medium-high heat. Once hot, add pineapple and stir fry until caramelized, about 3 minutes; remove pineapple to a plate.
Heat 1 tablespoon vegetable oil in the now empty skillet over medium-high heat. Add the chicken (discard marinade) and stir fry just until the outsides are no longer pink, about 2-3 minutes (chicken will not be cooked through; don’t overcook). Remove chicken to a plate.
To the now empty pan (don’t wipe out), heat another drizzle of oil over medium-high heat. Add broccoli, carrots, and bell peppers. Stir fry until vegetables are crisp tender, about 2 minutes. (Don’t over-cook because they will continue to cook in sauce.)
Return the chicken and pineapple to the skillet. Whisk the sauce to recombine then add to the skillet. Cook, stirring constantly, until the sauce is thickened, the chicken is cooked and vegetables are crisp tender, about 2 minutes, taking care not to overcook the chicken.
Stir in about half of the green onions. Taste and add additional chili sauce for spicier, vinegar for tangier, or a sprinkle of sugar for sweeter. Serve with rice and garnish with remaining green onions.