Take the sirloin steak out of the refrigerator about 20 minutes before cooking to reach room temperature. Pat it dry and season generously with salt and black pepper on both sides.
Preheat a heavy skillet (preferably cast iron) over medium-high heat. Once hot, sear the steak for about 3-4 minutes on each side for medium-rare, or adjust cooking times to your preferred doneness.
Meanwhile, preheat your oven to 400°F. Wash the sweet potato and cut it into cubes. Toss the cubes with olive oil, a pinch of salt, and pepper, then spread them out on a baking sheet.
Roast the sweet potatoes in the oven for 20-25 minutes, stirring halfway through, until tender and lightly caramelized.
While the steak and sweet potatoes are cooking, steam the broccoli. Place broccoli florets in a steamer over boiling water and steam for about 5-7 minutes until bright green and just tender.
Let the steak rest for about 5 minutes after searing, then slice against the grain. Plate the sliced steak alongside the roasted sweet potatoes and steamed broccoli.
Serve immediately while warm and enjoy your balanced, flavorful dinner.