Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Wash and dice the russet potato into 1-inch cubes, ensuring they are uniform in size for even roasting.
Slice the chicken breast into bite-sized pieces and trim the ends of the green beans.
Mince the garlic cloves and finely chop the fresh rosemary leaves.
In a large mixing bowl, combine the chicken, potatoes, and green beans with the olive oil, minced garlic, rosemary, sea salt, and black pepper.
Toss the ingredients thoroughly until every piece is evenly coated in the oil and aromatics.
Spread the mixture in a single layer on the prepared baking sheet, ensuring the pieces are not overcrowded.
Roast in the center of the oven for 22 to 25 minutes, or until the potatoes are golden-brown and the chicken reaches an internal temperature of 165°F.
Remove from the oven and let rest for 2 minutes before serving to allow the juices to redistribute.