In a small bowl, whisk together the smoked paprika, garlic powder, onion powder, dried thyme, dried oregano, cayenne pepper, sea salt, and black pepper to create the Cajun rub.
Pat the catfish fillets completely dry with a paper towel, then coat both sides of the fish generously with the spice mixture, pressing it in so it adheres.
Heat a cast-iron skillet over medium-high heat and add 0.5 tbsp of avocado oil, swirling to coat the bottom.
Place the catfish fillets in the hot skillet and sear for 3 to 4 minutes per side until a dark, crispy crust forms and the fish is opaque and flakes easily with a fork.
While the fish is searing, steam the green beans or sauté them in a separate pan with the remaining 0.5 tbsp of avocado oil until they are bright green and tender-crisp.
Plate the blackened catfish over the fluffy cooked quinoa, serve the green beans on the side, and finish with a fresh squeeze of lemon juice over the fish.