In a small bowl, combine the smoked paprika, onion powder, garlic powder, dried thyme, dried oregano, cayenne pepper, sea salt, and black pepper to create the Cajun rub.
Pat the catfish fillets completely dry with paper towels, then coat both sides of the fish generously with the spice mixture.
Prepare the lemon aioli by whisking together the avocado oil mayonnaise, lemon juice, and lemon zest in a small ramekin until smooth.
Steam the green beans in a steamer basket over boiling water for 5-6 minutes until they are tender-crisp and bright green.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until it begins to shimmer.
Carefully place the catfish fillets in the hot skillet and sear for 3-4 minutes per side until the spice crust is dark and the fish flakes easily with a fork.
Plate the blackened catfish alongside the steamed green beans and serve with a dollop of the lemon aioli on top of the fish.