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