Pat the catfish fillets completely dry with paper towels to ensure a proper sear.
In a small bowl, combine the smoked paprika, garlic powder, onion powder, dried thyme, dried oregano, cayenne pepper, sea salt, and black pepper.
Coat both sides of the catfish fillets generously with the spice rub, pressing it into the flesh so it adheres well.
Prepare the lemon aioli by whisking together the avocado oil mayonnaise, Greek yogurt, lemon juice, lemon zest, and one minced garlic clove in a small ramekin.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until it begins to shimmer.
Place the catfish fillets in the hot skillet and cook for 3 to 4 minutes per side, or until the spices have formed a dark, blackened crust and the fish is opaque and flakes easily.
While the fish cooks, steam the green beans for 5 to 6 minutes until they are bright green and tender-crisp.
Plate the blackened catfish alongside the steamed green beans and serve with a dollop of the lemon aioli on top.