Preheat your oven to 400°F (200°C) and line a small baking sheet with parchment paper.
In a mixing bowl, toss the broccoli florets, sliced red bell pepper, and red onion with 0.5 tbsp of olive oil, 0.25 tsp salt, and 0.25 tsp garlic powder.
Spread the vegetables in a single layer on the baking sheet and roast for 15-20 minutes until tender and slightly charred.
While the vegetables roast, pat the steak dry with paper towels and season both sides with the remaining salt, pepper, and finely chopped fresh rosemary.
Heat the remaining 0.5 tbsp of olive oil in a cast-iron skillet over medium-high heat until the oil is shimmering.
Place the steak in the hot skillet and sear for 3-4 minutes per side for medium-rare, or until it reaches your preferred internal temperature.
Remove the steak from the pan and let it rest for 5 minutes on a cutting board before slicing against the grain.
Plate the sliced steak alongside the roasted vegetables and serve immediately.