Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper for easy cleanup.
Dice the chicken breast and the russet potato into uniform 1-inch cubes to ensure they cook evenly.
Mince the garlic cloves and finely chop the fresh rosemary leaves.
In a large mixing bowl, combine the chicken, potatoes, and broccoli florets.
Drizzle the olive oil over the mixture and add the minced garlic, rosemary, sea salt, black pepper, and onion powder.
Toss everything thoroughly until the chicken and vegetables are well-coated in the oil and seasonings.
Spread the mixture in a single layer on the prepared baking sheet, ensuring the pieces aren't too crowded so they can crisp up.
Roast in the oven for 25 to 30 minutes, tossing the ingredients halfway through, until the potatoes are tender and the chicken is cooked through.