Prepare all your ingredients before you start cooking. Slice the chicken into thin, even pieces so it cooks quickly and evenly. Break the broccoli into bite-sized florets and rinse well. Have garlic, ginger, soy sauce, oyster sauce, vinegar, sugar, and cornstarch measured and ready to go near the stove.

In a small bowl, whisk together the soy sauce, oyster sauce, rice vinegar, sugar, and cornstarch until smooth. This is your stir-fry sauce; set it aside. If you’re omitting oyster sauce, you can add another dash of soy and a splash of water later to reach a similar sauciness.

Heat 1 tablespoon of oil in a large skillet or wok over medium-high heat. Once the oil shimmers, add the chicken in a single layer. Let it sear without disturbing for about 1–2 minutes to brown, then flip and cook another 1–2 minutes until the chicken is just cooked through. Remove to a plate and set aside.

In the same pan, add the remaining oil. Add the garlic and ginger, stirring quickly for about 30 seconds until fragrant. Be careful not to burn them.

Add the broccoli (and bell pepper, if using) to the pan. Stir-fry for 3–4 minutes, until the broccoli is bright green and crisp-tender. If your pan seems dry, splash in a tiny bit of water to create steam and help the vegetables cook evenly.

Return the chicken to the pan. Pour in the prepared sauce and toss to coat, letting it simmer for 1–2 minutes until the sauce thickens and everything is glossy. If the sauce thickens too much, add a splash more water or broth to reach your desired consistency.

Finish with a light drizzle of sesame oil and toss once more. Taste and adjust seasoning with a pinch of salt or pepper if needed. Turn off the heat and sprinkle with green onions for color and a fresh bite.

Serve immediately over steamed rice, quinoa, or noodles. Leftovers will keep in the fridge for up to 3 days and can reheat gently on the stove or in the microwave with a splash of water to loosen the sauce.