Pat the catfish fillets completely dry with a paper towel to ensure a proper sear.
In a small bowl, whisk together the smoked paprika, garlic powder, onion powder, thyme, oregano, cayenne, sea salt, and black pepper.
Press the spice mixture firmly onto both sides of the catfish fillets until evenly coated.
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 skillet and sear for 3 to 4 minutes per side until a dark, flavorful crust forms and the fish flakes easily with a fork.
Remove the fish from the skillet and set aside; in the same pan, add the cauliflower rice and diced bell peppers.
Sauté the vegetables for 4 to 5 minutes, scraping up any remaining spices from the bottom of the pan, until tender-crisp.
Divide the cauliflower rice onto plates and top with the blackened catfish fillets.