Warm up the oil in a 12-inch nonstick skillet over medium heat for about a minute, just until it’s hot but not smoking.
Toss in the green beans, sprinkle with salt and pepper, and cook, stirring now and then with a rubber spatula, until the beans start to develop some brown spots, roughly 4 to 6 minutes.
Carefully add water to the skillet, then cover it with a lid. Steam the beans until they turn a vibrant green, which should take about 2 minutes. Be sure to use an oven mitt when removing the lid—watch out for the steam!
Turn up the heat to medium-high and cook until the water evaporates, which should take around a minute.
Mix in the butter and garlic, and continue cooking, stirring frequently, until the green beans are nicely browned, another 2 to 4 minutes. Turn off the heat and use the spatula to move the green beans to a serving dish. They’re ready to serve.