In a small bowl, whisk together the smoked paprika, garlic powder, onion powder, dried thyme, dried oregano, cayenne pepper, sea salt, and black pepper to create the blackening seasoning.
Pat the catfish fillets completely dry with a paper towel and coat both sides generously with the spice blend, pressing it into the flesh.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until it is shimmering and just beginning to smoke.
Carefully place the catfish in the hot skillet and sear for 3 to 4 minutes per side until the crust is dark and charred and the fish flakes easily with a fork.
While the fish is searing, mix the avocado oil mayonnaise, lemon juice, and lemon zest in a small ramekin until smooth.
Steam the green beans for 5 minutes until tender-crisp and bright green.
Plate the blackened catfish alongside the green beans and serve with the lemon aioli on the side.