In a small bowl, combine the smoked paprika, garlic powder, onion powder, dried thyme, dried oregano, cayenne pepper, sea salt, and black pepper to create the blackening seasoning.
Pat the catfish fillets completely dry with paper towels, then coat both sides evenly with the spice mixture, pressing it gently into the flesh.
Prepare the lemon aioli by whisking together the plain Greek yogurt, lemon juice, and minced garlic in a small ramekin until smooth.
Heat the ghee in a cast-iron skillet over medium-high heat until it is shimmering and very hot.
Carefully place the catfish fillets in the hot skillet and sear for approximately 3 to 4 minutes per side, or until the spice crust is dark and charred and the fish flakes easily with a fork.
While the fish is searing, steam the asparagus spears for 4 to 5 minutes until they are bright green and tender-crisp.
Plate the blackened catfish alongside the steamed asparagus and top each fillet with a dollop of the lemon-garlic aioli.