In a small bowl, whisk together the Greek yogurt, Dijon mustard, lemon juice, and pickle juice to create the zesty remoulade.
Combine the smoked paprika, garlic powder, onion powder, oregano, thyme, cayenne, salt, and pepper in a shallow dish to make the blackened seasoning.
Pat the catfish fillet completely dry with a paper towel and coat both sides generously with the spice blend, pressing it into the flesh.
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 3-4 minutes per side until a dark crust forms and the fish flakes easily with a fork.
While the fish is searing, steam the green beans in a steamer basket for 5-6 minutes until they are bright green and tender-crisp.
Plate the blackened catfish immediately, topped with a generous dollop of the remoulade and the steamed green beans on the side.