Coat the chicken: Toss the thinly sliced chicken with 1 tablespoon of the cornstarch and 1 tablespoon of the soy sauce until every piece is lightly coated. Let it sit for 10 minutes while you prep everything else.

Whisk the garlic ginger sauce: In a small bowl, whisk the remaining 1 tablespoon cornstarch with the remaining 3 tablespoons soy sauce until smooth and lump-free. Whisk in the chicken broth, rice vinegar, honey, toasted sesame oil, and red pepper flakes if using. Set it near the stove.

Steam the broccoli in the skillet: Heat 1 tablespoon of the vegetable oil in a large skillet or wok over medium-high heat. Add the broccoli and stir for 2 minutes, then pour in the water, cover, and steam for 3 minutes until the florets are bright green and crisp-tender. Transfer them to a plate and wipe the skillet dry.

Sear the chicken: Add the remaining 2 tablespoons vegetable oil to the skillet over high heat. Spread the chicken in a single layer and leave it undisturbed for 1 minute, then toss and cook 3-4 minutes more, until browned and a thermometer reads 165°F. Cook in two batches if the pan is crowded.

Bloom the garlic and ginger: Reduce the heat to medium, push the chicken to one side, and add the minced garlic and grated ginger. Stir for 30-45 seconds, just until fragrant, then toss with the chicken.

Add the sauce: Whisk the sauce again to redistribute the cornstarch, pour it into the skillet, and stir constantly for 1-2 minutes until it thickens and turns glossy enough to coat the back of a spoon.

Return the broccoli and serve: Add the steamed broccoli back to the pan and toss for about 1 minute until everything is coated and hot. Spoon the chicken and broccoli stir fry over cooked white rice and top with sliced green onions and toasted sesame seeds.