Whisk together all sauce ingredients in a small mixing bowl
heat vegetable oil in a large pan on medium-high heat
When oil is shimmering, add chicken, season with salt and pepper, and fry til no longer pink, 3-5 minutes
Remove the chicken from the pan with a slotted spoon, leaving the juices
add the onions and peppers to the pan, stirring frequently til just starting to soften
add the garlic and continue to stir fry for an other 1-2 minutes, then remove with a slotted spoon
Add the sauce to the pan and bring the heat to high, once the sauce is simmering heavily, reduce heat to medium and simmer for 2-3 minutes til liquid reduces some
Use a flat bottom spoon to scrape the bottom of the pan and stir the sauce
add the chicken and veg back to the pan and continue to simmer on medium for anohter 3-5 minutes until sauce thickens