In a small bowl, whisk together the Greek yogurt, lemon juice, lemon zest, and Dijon mustard to create the aioli.
In another small bowl, combine the smoked paprika, garlic powder, onion powder, dried thyme, dried oregano, cayenne pepper, sea salt, and black pepper.
Pat the catfish fillets dry with a paper towel and coat both sides generously with the spice blend.
Heat the avocado oil in a 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 exterior is blackened and the fish flakes easily with a fork.
While the fish cooks, steam the green beans for 5 minutes until tender-crisp.
Serve the blackened catfish immediately with a dollop of lemon aioli and the green beans on the side.