Blanch the green beans: Bring a large pot of salted water to a boil. Add the green beans and blanch for about 3 minutes until they are bright green and slightly tender. Drain and immediately transfer them to a bowl of ice water to stop the cooking process. Drain again and set aside.
Prepare the sauce: In a small bowl, combine the minced garlic, sesame oil, soy sauce, and red pepper flakes (if using). Mix well and set aside.
Sauté the green beans: In a large skillet, heat the olive oil over medium-high heat. Once hot, add the blanched green beans. Sauté for about 3-4 minutes until they are slightly caramelized and crisp-tender.
Add the sauce: Pour the garlic and sesame mixture over the green beans in the skillet. Stir well to combine and cook for an additional 2 minutes, allowing the flavors to meld together.
Finish with sesame seeds: Sprinkle the toasted sesame seeds over the green beans and stir to coat evenly. Season with salt to taste.
Garnish and serve: Transfer the green beans to a serving dish and garnish with sliced green onions.