In a large bowl, whisk together the lemon juice, garlic, mustard, salt, and several grinds of pepper. Stir in the thyme leaves.

Heat the olive oil in a large skillet over medium heat. Add the green beans and toss to coat. Add the water, cover, and cook for 5 minutes, or until the beans are tender but still have a slight bite. Transfer to the bowl with the lemon mixture and toss. Season to taste and transfer to a serving platter, leaving any excess water behind.