Begin by blanching the green beans: Bring a pot of water to a boil and add the trimmed green beans. Let them cook for about 3-4 minutes until they are bright green and tender-crisp.
Immediately transfer the green beans to a bowl of ice water to stop the cooking process. Let them cool for a couple of minutes before draining and patting dry.
In a large skillet or wok, heat the sesame oil over medium heat. Once hot, add the minced garlic and cook for about 1 minute until fragrant but not browned.
Add the blanched green beans to the skillet, tossing them well in the garlic oil. Sauté for about 2-3 minutes until they are heated through.
Drizzle the soy sauce and rice vinegar over the green beans, tossing to combine. Add chili flakes if desired and season with salt and pepper to taste.
Continue to cook for an additional 1-2 minutes, allowing the flavors to meld together.
Remove from heat and sprinkle sesame seeds on top, tossing gently to coat.
Serve warm, garnished with sliced scallions for a fresh finishing touch.