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 blackening seasoning.
Pat the catfish fillets completely dry with a paper towel and coat both sides generously with the prepared spice mixture, pressing the spices into the flesh.
Prepare the lemon aioli by whisking together the Greek yogurt, lemon juice, and Dijon mustard in a small ramekin until the mixture is smooth and creamy.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until it begins to shimmer and is very hot.
Carefully place the seasoned catfish fillets into the hot skillet and sear for 3 to 4 minutes per side until a dark crust forms and the fish flakes easily with a fork.
While the fish is searing, steam the broccoli florets in a steamer basket over boiling water for 4 to 5 minutes until they are vibrant green and tender-crisp.
Plate the blackened catfish immediately, topped with a dollop of the lemon aioli, and serve alongside the steamed broccoli.