Oven and Pan Setup: Adjust an oven rack to the middle position and preheat your oven to 400∘F (200∘C). Lightly grease a large, rimmed baking sheet with 1 tsp of olive oil or coat with cooking spray.
Prepare the Vegetable Medley: Scatter the cut asparagus, orange bell pepper, yellow squash, red onion, and cherry tomatoes in an even layer on the prepared baking sheet. Tuck the fresh rosemary sprigs amongst the vegetables.
Concoct the Herb Butter: In a small bowl, thoroughly combine the melted unsalted butter with the garlic powder, salt, ground black pepper, and smoked paprika.
Season the Components: Drizzle about half of the herb butter mixture over the vegetables on the baking sheet. Gently toss the vegetables to ensure they are lightly coated. Push the vegetables towards the outer edges of the pan to create a clear space in the center. Lay the sirloin steak in this central space. Brush the remaining herb butter generously over all surfaces of the steak.
Roast to Perfection: Carefully place the baking sheet into the hot oven. Roast for 25-35 minutes. The precise cooking duration will vary based on your steak's thickness and your desired internal temperature. For best results, use a meat thermometer (see the nots)
Rest Steak, Then Serve: Once the steak reaches your preferred doneness, remove it from the baking sheet and transfer it to a clean cutting board. Tent the steak loosely with aluminum foil and allow it to rest for 5-10 minutes. This resting period is crucial for the juices to redistribute, resulting in a more tender and flavorful steak. After resting, slice the sirloin against the grain. Serve the sliced steak alongside the roasted rainbow veggie feast.