In a small bowl, whisk together the smoked paprika, garlic powder, onion powder, thyme, oregano, cayenne, sea salt, and black pepper.
Pat the catfish fillets dry with paper towels and coat both sides generously with the prepared spice mixture.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until shimmering.
Place the catfish in the skillet and sear for 3-4 minutes per side until the crust is blackened and the fish flakes easily with a fork.
While the fish cooks, prepare the sauce by mixing the Greek yogurt, chopped fresh dill, and lemon juice in a small bowl.
Steam the green beans until tender-crisp, approximately 5 minutes.
Serve the blackened catfish immediately, topped with a dollop of lemon-dill sauce and the green beans on the side.