Prep the chicken: Pat the chicken dry and slice into thin strips. Toss with 1 tablespoon cornstarch, a pinch of salt, and a few grinds of pepper.
This helps it brown and stay tender.
Make the sauce: In a small bowl, whisk sweet chili sauce, soy sauce, rice vinegar, lime juice, sesame oil, remaining 1 tablespoon cornstarch, and water or broth. Taste and adjust heat with red pepper flakes or sriracha if you like it spicier.
Heat the pan: Set a large skillet or wok over medium-high heat. Add 1–2 tablespoons oil and swirl to coat.
Sear the chicken: Add chicken in a single layer.
Cook 3–4 minutes, flip, and cook another 2–3 minutes until browned and just cooked through. Transfer to a plate. Do not overcrowd; cook in batches if needed.
Stir-fry the veggies: Add another splash of oil.
Add broccoli and carrots first; cook 2 minutes, stirring. Add bell pepper and peas; cook 2–3 minutes more until crisp-tender.
Aromatics in: Push veggies to the sides. Add garlic, ginger, and the white parts of green onions to the center.
Stir 30 seconds until fragrant.
Combine and sauce: Return chicken and any juices to the pan. Whisk the sauce again, then pour it in. Toss everything to coat.
Cook 1–2 minutes until the sauce is glossy and slightly thickened.
Finish: Remove from heat. Sprinkle with sesame seeds and green onion tops. Add cilantro if using.
Serve over hot rice or noodles with lime wedges.