Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Wash the russet potato and dice into 1-inch cubes, then trim the ends of the green beans.
Mince the garlic cloves and finely chop the fresh rosemary leaves.
In a large mixing bowl, toss the potato cubes with half of the olive oil, half of the minced garlic, half of the rosemary, and a pinch of the salt and pepper.
Spread the potatoes in a single layer on the baking sheet and roast for 15 minutes.
While the potatoes roast, cut the top sirloin steak into 1-inch bite-sized pieces and toss them in the same mixing bowl with the remaining oil, garlic, rosemary, salt, pepper, and the green beans.
Remove the baking sheet from the oven, slide the potatoes to one side, and add the beef and green beans to the other side.
Return the sheet to the oven and roast for an additional 10 to 12 minutes until the beef is cooked to your preferred level of doneness and the potatoes are golden.
Let the beef rest on the pan for 2 minutes before serving to ensure it stays juicy.