In a small bowl, whisk together the Greek yogurt, lemon juice, minced garlic, and Dijon mustard to create the aioli; set aside in the refrigerator.
In a shallow dish, combine the smoked paprika, garlic powder, onion powder, oregano, thyme, cayenne, sea salt, and black pepper.
Pat the catfish fillets dry with a paper towel and dredge both sides thoroughly in the spice mixture, pressing gently to adhere.
Heat the olive oil in a cast-iron skillet over medium-high heat until shimmering.
Place the catfish in the hot 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, steam the green beans for 5 minutes until vibrant and tender-crisp.
Serve the blackened catfish immediately with a dollop of lemon aioli and the steamed green beans on the side.