Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Trim the woody ends off the asparagus and place them on the baking sheet, tossing with half of the olive oil and a pinch of salt and pepper.
In a small bowl, combine the smoked paprika, garlic powder, onion powder, dried oregano, cayenne pepper, sea salt, and black pepper to create the blackened seasoning.
Pat the salmon fillet completely dry with a paper towel and coat the top flesh side generously with the spice blend, pressing it in slightly.
Heat the remaining olive oil in a cast-iron or oven-safe skillet over medium-high heat.
Once the pan is hot, sear the salmon flesh-side down for 2-3 minutes until a dark, flavorful crust forms, then carefully flip the fillet.
Place the skillet in the oven alongside the asparagus and roast for 8-10 minutes until the salmon is flaky and the asparagus is tender-crisp.
Remove from the oven and finish with a fresh squeeze of lemon juice over the salmon and greens before serving.