In a small bowl, whisk together the smoked paprika, garlic powder, onion powder, cayenne pepper, dried thyme, dried oregano, sea salt, and black pepper.
Pat the catfish fillets completely dry with a paper towel and coat both sides generously with the spice rub, pressing it into the flesh.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until the oil is shimmering and just starting to smoke.
Carefully place the catfish fillets in the hot skillet and sear for 3 to 4 minutes per side until a dark, flavorful crust forms and the fish flakes easily.
While the fish cooks, steam the cauliflower rice and green beans in a separate pan with a splash of water until tender-crisp.
Plate the blackened catfish over the cauliflower rice with the green beans on the side, finishing with a fresh squeeze of lemon juice.