In a small bowl, combine the smoked paprika, garlic powder, onion powder, cayenne pepper, dried oregano, sea salt, and black pepper.
Pat the catfish fillets completely dry with paper towels and coat both sides generously with the spice rub.
Prepare the lemon aioli by whisking together the Greek yogurt, lemon juice, minced garlic clove, and Dijon mustard in a small ramekin until smooth.
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 to 4 minutes per side until the crust is blackened and the fish flakes easily with a fork.
While the fish cooks, steam the green beans in a steamer basket over boiling water for 5 minutes until they are bright green and crisp-tender.
Serve the blackened catfish immediately with a dollop of lemon aioli and the steamed green beans on the side.