In a small bowl, combine the smoked paprika, garlic powder, onion powder, dried thyme, dried oregano, cayenne pepper, sea salt, and black pepper to create the blackening spice rub.
Pat the catfish fillet completely dry with a paper towel, then coat both sides generously with the prepared spice rub, pressing it into the flesh.
In a small ramekin, whisk together the avocado oil mayonnaise, lemon juice, and lemon zest until smooth to create the aioli.
Steam the green beans in a steamer basket over boiling water for 5-6 minutes until they are bright green and crisp-tender.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until shimmering but not smoking.
Place the catfish in the hot skillet and sear for 3-4 minutes per side until the crust is dark and the fish flakes easily with a fork.
Plate the blackened catfish alongside the steamed green beans and serve immediately with a dollop of the lemon aioli.