Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Scrub the russet potato clean and cut it into small 1/2-inch cubes to ensure they roast quickly.
Cut the chicken breast into bite-sized pieces, roughly the same size as the potato cubes.
Mince the garlic clove and finely chop the fresh rosemary leaves.
In a large mixing bowl, combine the chicken, potatoes, and broccoli florets.
Drizzle with extra virgin olive oil and sprinkle with the minced garlic, rosemary, sea salt, and black pepper.
Toss everything thoroughly until the ingredients are evenly coated in the oil and seasonings.
Spread the mixture in a single layer on the prepared baking sheet, ensuring no pieces are overlapping.
Roast in the oven for 20 to 25 minutes, tossing halfway through, until the chicken reaches an internal temperature of 165°F and the potatoes are fork-tender and golden.
Remove from the oven and serve immediately while hot and crispy.