In a small bowl, whisk together the Greek yogurt, Dijon mustard, lemon juice, and minced capers to create the zesty remoulade sauce.
In a shallow dish, combine the smoked paprika, garlic powder, onion powder, cayenne, dried thyme, sea salt, and black pepper.
Pat the catfish fillets completely dry with a paper towel and coat both sides generously with the spice mixture, pressing it in to adhere.
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 a dark, crispy crust forms and the fish flakes easily with a fork.
While the fish is searing, steam the green beans for 4 to 5 minutes until they are bright green and crisp-tender.
Serve the blackened catfish immediately with a side of steamed green beans and a dollop of the prepared remoulade.