Pat the salmon fillet completely dry with paper towels to ensure a crispy, restaurant-quality sear.
In a small bowl, whisk together the smoked paprika, garlic powder, onion powder, cayenne, sea salt, and black pepper to create the Cajun rub.
Evenly coat the flesh side of the salmon with the spice mixture, pressing it gently so it adheres to the fish.
Heat the avocado oil in a cast-iron or heavy-bottomed skillet over medium-high heat until it begins to shimmer.
Carefully place the salmon in the pan, spice-side down, and sear for 3-4 minutes without moving it until a dark, flavorful crust forms.
Flip the salmon carefully and cook for an additional 2-3 minutes on the skin side until the fish is opaque and flakes easily.
While the salmon finishes, steam the asparagus spears for 4-5 minutes until they are bright green and tender-crisp.
Remove the salmon from the heat, squeeze the fresh lemon juice over the top, and serve immediately with the steamed asparagus.