Preheat the oven to 425 degrees and line a large baking sheet with parchment paper or foil.
In a large bowl, whisk together the olive oil, minced garlic, lemon juice, salt, pepper, and oregano.
Add the chicken thighs and halved potatoes to the bowl. Toss until everything is coated.
Spread the chicken and potatoes in a single layer on the prepared baking sheet. Place the pan in the oven and roast for 20 minutes.
Remove the pan from the oven and add the green beans around the chicken and potatoes. Return the pan to the oven.
Roast for another 15 to 20 minutes until the chicken reaches 165 degrees and the potatoes are golden.
Remove from the oven and top with lemon slices and chopped parsley before serving.