Heat half a tablespoon of oil in a large pan over medium heat.
Add prepared veggies and stir fry for 3-4 minutes, until just beginning to get tender. Set aside.
To the same preheated skillet add garlic, ginger, and fry for 1 minute. Add in the chicken and cook, stirring frequently, until golden and cooked through.
Meanwhile, in a small bowl, combine the soy sauce, honey, Worcestershire, vinegar, tomato paste, and cornstarch. Whisk well until cornstarch is fully dissolved.
Pour this mixture over the cooked chicken and stir to coat, allowing it to simmer for a couple of minutes; You'll see it begins to thicken almost immediately.
Return the cooked veggies back to the pan, together with the pineapple chunks.
Toss everything to combine and coat with the sauce.
Sprinkle with sesame seeds and green onion and serve over cooked rice, if desired.