In a small bowl, combine the smoked paprika, garlic powder, onion powder, dried oregano, cayenne pepper, sea salt, and black pepper to create the Cajun rub.
Pat the catfish fillets completely dry with a paper towel and coat both sides generously with the spice mixture, pressing it firmly into the flesh.
Prepare the lemon aioli by whisking together the avocado oil mayonnaise, lemon juice, lemon zest, and minced garlic in a small ramekin until smooth.
Heat a cast-iron skillet over medium-high heat with the avocado oil until the oil is shimmering and just starting to smoke.
Carefully place the catfish 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, sauté the green beans in a separate pan with the ghee and a tablespoon of water for about 5 minutes until they are bright green and crisp-tender.
Plate the blackened catfish alongside the sautéed green beans and serve with a dollop of the lemon aioli on top.