Melt the butter in a large, deep skillet over medium-high heat. When it starts foaming, add the beans. Cook them, stirring to coat them in the butter, for 1 minute.
Season the beans with kosher salt, garlic powder, and dried thyme. Cook, stirring, for 3 minutes.
Add ¼ cup of water to the pan and cover.
Reduce the heat to medium. Cook the beans until tender-crisp, for 4-5 minutes.
Remove the lid. Season the beans with freshly ground black pepper. Stir in the lemon juice.
Transfer the beans to a serving plate using tongs or a slotted spoon. Serve immediately.
Video
Notes
I opt to saute the haricot verts in butter, add water, and cover the pan. This is an easier method than blanching the beans (briefly submerging them in boiling water and then plunging them into ice water) and then sauteing them, and it produces comparable results.
You can use frozen beans, but the result won't be as good. It's best to use fresh beans. If you opt for frozen, you don't need to thaw them first.
You can keep the leftovers in an airtight container in the fridge for up to five days. Reheat them covered in the microwave or uncovered in a 350°F oven. You can also freeze them for up to three months.