Wash and scrub the potatoes. Cut them into 1-inch cubes or wedges for even roasting.
In a bowl, toss the potatoes with 2 tablespoons of olive oil, garlic powder, rosemary (or thyme), salt, and pepper.
Spread the potatoes out on one side of the prepared sheet pan, making sure they’re in a single layer.
Prepare the Chicken:

In a small bowl, mix together the olive oil, garlic powder, onion powder, thyme (or rosemary), paprika, salt, and pepper.
Rub the mixture all over the chicken breasts (or thighs). Optionally, drizzle with lemon juice for extra flavor.
Place the chicken on the sheet pan, next to the potatoes. Make sure the chicken is spaced out to allow even cooking.
Roast the Potatoes and Chicken:

Place the sheet pan in the oven and roast for about 25-30 minutes, or until the chicken reaches an internal temperature of 165°F (75°C) and the potatoes are tender and golden. Stir the potatoes halfway through to ensure even cooking.
Prepare the Green Beans:

While the chicken and potatoes are roasting, prepare the green beans. Toss them in olive oil, salt, pepper, and garlic powder (if using).
After the potatoes have been roasting for 25 minutes, remove the sheet pan from the oven. Push the potatoes and chicken to one side to make room for the green beans.
Add the green beans to the sheet pan and return it to the oven for an additional 10-15 minutes, or until the green beans are tender and slightly caramelized.