Prep the beans: Rinse and trim the green beans. Pat them dry so they sear instead of steam.
Make the sauce: In a small bowl, whisk soy sauce, oyster sauce, rice vinegar, sugar, chili garlic sauce, water, and cornstarch.
Set aside.
Heat the pan: Place a large skillet or wok over medium-high to high heat. Add the oil and let it shimmer.
Blister the beans: Add the green beans in a single layer. Cook 4–6 minutes, stirring every 30 seconds, until they develop charred spots but stay crisp-tender.
Aromatics in: Push beans to the sides.
Add a splash of oil if needed. Stir in garlic, ginger, and the scallion whites. Cook 30–45 seconds until fragrant.
Sauce it up: Give the sauce a quick stir (cornstarch settles).
Pour it into the pan. Toss constantly for 1–2 minutes until the sauce thickens and coats the beans.
Finish: Turn off the heat. Stir in sesame oil and the scallion greens.
Taste and adjust salt, heat, or sweetness.
Serve: Transfer to a plate. Sprinkle sesame seeds and squeeze a little lime if you like. Eat hot with rice or noodles.