Preheat the oven to 425°F and line a large baking sheet with parchment paper or foil for easy cleanup.
Juice one lemon into a small bowl and add the olive oil, minced garlic, thyme, rosemary, salt, and pepper. Stir to combine.
Place the halved potatoes in a mixing bowl and toss with half of the lemon-herb mixture until evenly coated.
Arrange the chicken thighs on the baking sheet and brush them with the remaining lemon-herb mixture. Scatter the potatoes around the chicken.
Roast for 25 minutes. Remove the pan from the oven, add the green beans, and toss them lightly with the pan juices.
Return the pan to the oven and roast for another 15 to 20 minutes, until the chicken reaches 165°F and the potatoes are tender.
Slice the remaining lemon and place the slices over the finished dish. Sprinkle with chopped parsley before serving.