Step 1

Whisk all the ingredients together in a small bowl, making sure the cornstarch is dissolved; set aside.

Step 2

Heat a flat-bottomed wok or large frying pan over medium-high heat until a drop of water vaporizes immediately on contact. Drizzle 1 tablespoon of the oil around the pan, and then add the garlic. Cook, stirring constantly with a metal spatula, until fragrant, about 10 seconds. Push the garlic to the side of the pan.

Step 3

Add about 1/2 of the chicken in a single layer and season with salt. Cook undisturbed for 1 minute, letting it sear. Stir-fry the chicken until lightly browned and cooked through, 3 to 4 minutes. Transfer the chicken to a large plate. Drizzle 1 tablespoon of the oil around the pan and repeat with the remaining chicken.

Step 4

Drizzle 1 tablespoon of the oil around the pan, add the broccoli, and season with salt. Stir-fry until it begins to soften and brown around the edges, 1 to 2 minutes. Transfer to the plate with the chicken.

Step 5

Drizzle the remaining 1/2 tablespoon of oil around the pan, add the peppers and zucchini, and season with salt. Stir-fry until browned and softened, 1 to 2 minutes.

Step 6

Add the reserved chicken and broccoli and any accumulated juices back to the pan and stir to combine. Stir the sauce one more time, pour into the pan, and stir-fry until the sauce is thickened and coats the chicken and vegetables, 1 to 2 minutes. Serve over rice or noodles and top with the the scallions.