1. Blanch green beans in a large pot of salted water until tender, 5 minutes. Drain and transfer to a large plate or rimmed baking sheet to cool.

2. Heat oil in a large skillet over medium-high. Add garlic and cook until softened and just beginning to color, 1 to 2 minutes. Add green beans and season generously with salt and pepper. When green beans are hot, toss in lemon slices and cook 1 minute over high. Check seasoning -- beans should be well-seasoned and bright but not too sour. Serve hot, or preferably at room temperature.