Prep the chicken. Trim any excess fat and slice the chicken thighs into thin strips, about 1/2 inch wide. Pat dry with paper towels for better browning.

Mix the sauce. In a bowl, whisk soy sauce, oyster sauce, rice vinegar, brown sugar, sesame oil, red pepper flakes (if using), and chicken broth. In a separate small bowl, stir cornstarch with 2 tablespoons of the sauce until smooth, then whisk that slurry back into the sauce. This prevents clumps.

Prep the veggies. Slice everything so it cooks quickly and evenly. Keep firmer veggies (broccoli, carrots) separate from quicker-cooking ones (peppers, peas, onions).

Heat the pan. Set a large skillet or wok over medium-high to high heat. Add 1 tablespoon oil and let it get hot—just starting to shimmer.

Sear the chicken in batches. Add half the chicken in a single layer. Don’t stir for 1–2 minutes so it browns, then stir-fry until cooked through, about 3–4 minutes total. Transfer to a plate and repeat with the remaining chicken, adding more oil if needed. Don’t crowd the pan.

Stir-fry the firm veggies. Add another teaspoon of oil if the pan is dry. Toss in broccoli and carrots. Stir-fry for 2–3 minutes until they brighten and start to soften.

Add quicker-cooking veggies and aromatics. Add onion and bell pepper. Stir-fry 2 minutes. Push veggies to the edges, add a splash of oil to the center, then add garlic and ginger. Stir 30 seconds until fragrant—avoid burning.

Return chicken and add sauce. Pour in the sauce and bring it to a simmer. It will thicken in 30–60 seconds. If using snap peas, add them now so they stay crisp.

Toss and finish. Stir to coat everything evenly. Cook 1 more minute, then turn off the heat. Sprinkle in green onions and a few sesame seeds if you like.

Taste and adjust. Add a splash more soy for salt, vinegar for brightness, or a pinch of sugar if it’s too salty. Serve hot over rice or noodles.