Preheat your oven to 425°F (220°C). A hot oven is crucial for achieving that crispy chicken skin.
In a mixing bowl, add the chicken thighs. Drizzle with 2 tablespoons of olive oil, then sprinkle with garlic powder, onion powder, smoked paprika, salt, and pepper. Toss to coat the chicken evenly with the seasoning mixture.
In the same bowl, add the trimmed green beans. Drizzle with the remaining tablespoon of olive oil and season with a bit more salt and pepper. Toss until the green beans are nicely coated.
Place the seasoned chicken thighs on one side of the sheet pan, skin side up. Spread the green beans out on the other side of the pan, ensuring they are in a single layer for even roasting.
Put the sheet pan in the preheated oven and roast for about 35-40 minutes, or until the chicken reaches an internal temperature of 165°F (74°C) and is golden brown. The green beans should be tender yet crisp.
Once done, remove the sheet pan from the oven. Let the chicken rest for a few minutes before serving. Squeeze fresh lemon juice over the chicken and green beans for a bright finish, if desired.