In a small bowl, combine the smoked paprika, garlic powder, onion powder, thyme, oregano, cayenne, sea salt, and black pepper to create the blackening seasoning.
Pat the catfish fillets completely dry with paper towels, then generously coat both sides with the spice mixture, pressing it into the flesh.
Prepare the lemon aioli by whisking together the avocado oil mayonnaise, lemon juice, lemon zest, and one finely minced garlic clove in a small ramekin.
Steam the green beans in a steamer basket over boiling water for 4-5 minutes until they are bright green and tender-crisp.
Heat the avocado oil in a large cast-iron skillet over high heat until it begins to shimmer and slightly smoke.
Carefully place the catfish fillets in the hot skillet and sear for 3-4 minutes per side until the crust is dark and charred and the fish flakes easily with a fork.
Plate the blackened catfish alongside the steamed green beans and serve immediately with a dollop of the lemon aioli.