Trim off both ends of the green beans, rinse under cold water, and pat completely dry with paper towels.

Heat a large skillet or wok over high heat for 2 minutes until it is smoking hot.

Add 1.5 tablespoons vegetable oil to the skillet, swirling until it shimmers; if it does not shimmer, wait an additional 30 seconds.

Add half of the green beans in a single layer and cook undisturbed for 2 minutes, then stir and cook for another 1 to 2 minutes until charred and tender-crisp; transfer to a plate.

Repeat cooking with the remaining 1.5 tablespoons oil and green beans, blistering them in the same manner, then return all beans to the skillet over medium-high heat.

In a small bowl, combine minced garlic, soy sauce, sesame oil, water, and sugar, stirring until the sugar dissolves.

Pour the garlic sauce over the beans and toss for 30 seconds until the beans are evenly coated and the sauce glazes them.

Season with red pepper flakes (if using), salt, and white pepper to taste, then transfer to a serving dish and serve warm.