Preheat your oven to 400°F and heat a grill pan or outdoor grill to medium-high heat.
On a large rimmed baking sheet, toss the broccoli florets, chopped bell peppers, and sliced red onion with half of the olive oil, half the sea salt, and the dried oregano.
Roast the vegetables in the oven for 15-20 minutes until they are tender and show slight charred edges.
While the vegetables roast, season both sides of the top sirloin steak with garlic powder, the remaining sea salt, and the black pepper.
Place the steak on the hot grill and cook for 4-5 minutes per side for medium-rare, or until it reaches your desired level of doneness.
Remove the steak from the grill and let it rest on a cutting board for at least 5 minutes before slicing against the grain.
In a small bowl, whisk together the remaining olive oil and lemon juice, then drizzle it over the roasted vegetables.
Plate the sliced steak alongside the zesty vegetables and serve immediately.