In a small bowl, whisk together the avocado oil mayonnaise, lemon juice, lemon zest, and one minced garlic clove to create the aioli.
In a separate small dish, 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 paper towels and coat both sides generously with the prepared Cajun spice mixture.
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 in a steamer basket over boiling water for 4 to 5 minutes until they are bright green and crisp-tender.
Transfer the blackened catfish to a plate alongside the steamed green beans and serve immediately with a dollop of the lemon aioli.