Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Trim the ends of the Brussels sprouts and cut them in half.
In a bowl, toss the halved Brussels sprouts with 0.75 tsp of olive oil and a pinch of the sea salt and black pepper.
Spread the sprouts in a single layer on the baking sheet and roast for 20-25 minutes until the edges are charred and crispy.
While the sprouts roast, pat the sirloin steak dry with a paper towel.
In a small bowl, combine the smoked paprika, garlic powder, onion powder, and the remaining sea salt and black pepper.
Rub the steak with the remaining 0.75 tsp of olive oil, then coat both sides evenly with the spice blend.
Heat a grill pan or outdoor grill over medium-high heat and sear the steak for 4-5 minutes per side for medium-rare.
Transfer the steak to a cutting board and let it rest for 5 minutes before slicing against the grain.
Remove the sprouts from the oven, drizzle with lemon juice, and serve immediately alongside the smoky steak.