In a small bowl, combine the smoked paprika, garlic powder, onion powder, dried oregano, cayenne pepper, sea salt, and black pepper to create the blackening spice.
Pat the catfish fillets completely dry with a paper towel and coat both sides generously with the prepared spice mixture.
Heat the avocado oil in a cast-iron skillet over medium-high heat until it begins to shimmer.
Carefully place the catfish in the hot skillet and sear for 3-4 minutes per side until a dark crust forms and the fish flakes easily with a fork.
While the fish is searing, whisk together the Greek yogurt, Dijon mustard, lemon juice, and chopped capers in a small bowl to make the remoulade.
Steam the green beans in a steamer basket over boiling water for 4-5 minutes until they are bright green and tender-crisp.
Serve the blackened catfish immediately topped with a dollop of the zesty remoulade and the steamed green beans on the side.