In a small bowl, combine the smoked paprika, garlic powder, onion powder, dried thyme, dried oregano, cayenne pepper, sea salt, and black pepper.
Pat the catfish fillets completely dry with a paper towel and coat both sides generously with the prepared Cajun spice blend.
In a separate small ramekin, whisk together the avocado oil mayonnaise, lemon juice, and lemon zest to create the aioli.
Heat the avocado oil in a cast-iron skillet over medium-high heat until it begins to shimmer.
Carefully place the catfish fillets in the hot skillet and sear for 3 to 4 minutes per side until a dark crust forms and the fish flakes easily with a fork.
While the fish is searing, steam the green beans until they are bright green and reach a crisp-tender texture.
Plate the blackened catfish immediately alongside the steamed green beans and top with a dollop of the lemon aioli.