In a small bowl, whisk together the Greek yogurt, Dijon mustard, lemon juice, hot sauce, and capers to create the remoulade; set aside in the refrigerator.
In a separate small bowl, mix the smoked paprika, garlic powder, onion powder, thyme, oregano, cayenne, sea salt, and black pepper to create the blackening seasoning.
Pat the catfish fillets completely dry with paper towels, then coat both sides of the fish generously with the spice mixture, pressing it in slightly.
Heat the avocado oil in a cast-iron or heavy-bottomed skillet over medium-high heat until it begins to shimmer.
Carefully place the catfish in the hot skillet and sear for 3 to 4 minutes per side until a dark crust forms and the fish is opaque and flakes easily.
While the fish is searing, steam the green beans for 4 to 5 minutes until they are bright green and tender-crisp.
Plate the blackened catfish alongside the steamed green beans and serve with a generous dollop of the prepared Cajun remoulade.