In a small bowl, whisk together the smoked paprika, garlic powder, onion powder, oregano, thyme, cayenne, sea salt, and black pepper.
Pat the catfish fillets completely dry with paper towels to ensure the spices adhere and create a crisp crust.
Evenly coat both sides of the fillets with the Cajun spice rub, pressing it firmly into the flesh.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until it begins to shimmer.
Carefully place the fillets in the hot skillet and sear for 3 to 4 minutes per side until the exterior is blackened and the fish flakes easily with a fork.
While the fish is searing, steam the green beans in a steamer basket for 5 minutes until they are tender-crisp and vibrant green.
Plate the blackened catfish alongside the green beans and serve immediately with a fresh lemon wedge for squeezing over the fish.