Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Dice the red potatoes into 1/2-inch cubes and toss them in a bowl with 1 tsp of olive oil, garlic powder, chopped rosemary, and half of the salt and pepper.
Spread the potatoes in a single layer on the baking sheet and roast for 20-25 minutes until golden and crispy.
Pat the sirloin steak dry with paper towels and season both sides with the remaining salt and pepper.
Heat the remaining 1 tsp of olive oil in a cast-iron skillet over medium-high heat until shimmering.
Place the steak in the skillet and sear for 3-4 minutes per side for medium-rare, or until it reaches your desired doneness.
Transfer the steak to a plate and let it rest for 5 minutes before slicing against the grain.
While the steak rests, steam the asparagus for 3-5 minutes until tender-crisp and bright green.
Plate the sliced steak alongside the roasted potatoes and steamed asparagus to serve.