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 Cajun rub.
Pat the catfish fillets completely dry with a paper towel and generously coat both sides with the spice mixture, pressing it in to ensure it adheres.
Heat 1 teaspoon of avocado oil in a large cast-iron skillet over medium-high heat until shimmering.
Place the catfish in the skillet and sear for 3-4 minutes per side until the crust is dark and crispy and the fish flakes easily with a fork.
Remove the fish from the pan and set aside; add the remaining 1 teaspoon of avocado oil along with the sliced red bell peppers and yellow onions.
Sauté the vegetables for 4-5 minutes until tender-crisp and slightly charred, then serve alongside the cooked quinoa and catfish fillets.
Finish the dish with a fresh squeeze of lemon juice for a bright, acidic pop that balances the smoky heat.