Pat the catfish fillets completely dry with a paper towel to ensure a proper sear.
In a small bowl, whisk together the smoked paprika, oregano, thyme, cayenne, onion powder, garlic powder, sea salt, and black pepper.
Coat both sides of the catfish fillets generously with the spice rub, pressing it into the flesh.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until it begins to shimmer.
Place the catfish in the skillet and sear for 3 to 4 minutes per side, or until the spice crust is blackened and the fish flakes easily with a fork.
While the fish cooks, steam the fresh green beans in a steamer basket for 5 minutes until tender-crisp and bright green.
In a small ramekin, stir together the avocado oil mayonnaise, lemon juice, and lemon zest to create the aioli.
Serve the blackened catfish immediately alongside the steamed green beans with a dollop of lemon aioli on top.