Wash the runner beans well. Trim the ends and slice on a slight diagonal for more surface area and better texture.
Bring a large pot of salted water to a rolling boil. Set a bowl of ice water nearby.
Drop the beans into the boiling water and cook for 2–3 minutes until bright green and crisp-tender.
Scoop the beans into the ice bath to stop cooking. Drain well and pat dry so the sauce sticks later.
Whisk soy sauce, rice vinegar, maple syrup, cornstarch, water, and red pepper flakes until smooth. No lumps means even thickening.
Heat the neutral oil in a large skillet or wok over medium-high heat.
Add garlic and ginger. Stir for 20–30 seconds until fragrant. Do not brown.
Add the blanched beans to the skillet. Toss for 1–2 minutes to rewarm and coat with aromatics.
Whisk the glaze again and pour it around the pan. Toss constantly as it thickens and turns glossy, about 30–60 seconds.
Turn off the heat. Drizzle with toasted sesame oil for a nutty finish.
Top with sesame seeds and scallions. Add a squeeze of lime if you like brightness.
Serve immediately while the beans stay glossy and crisp.
