Bring a medium, well-salted pot of water to a boil. Add the green beans to the boiling water and cook for 3-4 minutes, until beans are cooked through, but not soggy. Drain the water and cool in a bowl with ice water. Pat the beans dry.

Heat the olive oil in a large skillet. Add the walnuts, garlic, and vinegar to the pan; saute until fragrant, 1-2 minutes. Add the green beans, crushed red pepper flakes, kosher salt and ground black pepper to the skillet. Toss until combined and saute until crunchy and fragrant. 

Remove the beans from the skillet and toss with the herbs. Serve warm.