Blanch green beans in a large stockpot of well-salted boiling water until bright green in color and tender-crisp, roughly 2 minutes. Drain and shock in a bowl of ice water to stop cooking.
Heat a large heavy skillet over medium heat. Add the oil. Add the garlic and red pepper flakes and saute until fragrant, about 30 seconds.
Add the beans and continue to saute until coated in the oil and heated through about 5 minutes. Add lemon zest and season with salt and pepper.
