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 generously coat both sides with the spice mixture, pressing it into the flesh.
In another small bowl, whisk together the Greek yogurt, Dijon mustard, lemon juice, and capers to prepare the zesty remoulade sauce.
Heat the avocado oil in a cast-iron skillet over medium-high heat until it begins to shimmer.
Place the catfish in the hot skillet and sear for 3 to 4 minutes per side until a dark crust forms and the fish flakes easily with a fork.
Remove the fish from the pan and set aside; add the green beans to the same skillet with a splash of water, sautéing for 4 minutes until tender-crisp.
Serve the blackened catfish immediately with a dollop of the remoulade and the green beans on the side.