In a small bowl, combine the smoked paprika, garlic powder, onion powder, dried thyme, dried oregano, cayenne pepper, sea salt, and black pepper.
Pat the catfish fillet completely dry with paper towels and coat both sides generously with the spice blend.
Prepare the aioli by whisking together the avocado oil mayonnaise, lemon zest, lemon juice, and minced garlic in a small ramekin; set aside.
Heat the avocado oil in a cast-iron skillet over medium-high heat until it begins to shimmer.
Place the seasoned catfish in the hot skillet and sear for 3 to 4 minutes per side until a dark crust forms and the fish is opaque and flaky.
While the fish cooks, steam the green beans for 5 minutes until they are bright green and crisp-tender.
Serve the blackened catfish immediately with a dollop of lemon aioli on top and the green beans on the side.