Preheat your oven to 425°F (220°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Wash the red potatoes and cut them into uniform 1-inch chunks to ensure even cooking.
Trim the ends off the green beans and set them aside in a small bowl.
Pat the chicken thighs dry with a paper towel to help them brown effectively in the oven.
In a large mixing bowl, combine the chicken thighs and potato chunks with the olive oil, rosemary, garlic powder, sea salt, and black pepper, tossing until everything is well-coated.
Spread the chicken and potatoes onto the prepared baking sheet in a single layer, ensuring they aren't overcrowded.
Roast for 15 minutes, then remove the tray and add the green beans, tossing them quickly with the juices on the pan.
Return the tray to the oven and roast for an additional 10 to 15 minutes, or until the chicken reaches an internal temperature of 165°F and the potatoes are fork-tender and golden.
Let the chicken rest for 5 minutes before serving to keep the meat juicy.