In a small bowl, combine the smoked paprika, garlic powder, onion powder, thyme, oregano, sea salt, black pepper, and cayenne pepper to create the blackening seasoning.
Pat the catfish fillets completely dry with paper towels and coat both sides generously with the prepared spice rub, pressing it into the flesh.
Prepare the remoulade by whisking together the Greek yogurt, Dijon mustard, lemon juice, and finely chopped capers in a small ramekin until smooth.
Heat the avocado oil in a cast-iron skillet over medium-high heat until it begins to shimmer.
Place the catfish fillets in the hot skillet and sear for 3 to 4 minutes per side until the crust is dark and crispy and the fish flakes easily with a fork.
While the fish is finishing, heat the olive oil in a separate pan over medium heat and sauté the fresh spinach for 2 minutes until just wilted.
Serve the blackened catfish immediately over the bed of sautéed spinach, topped with a dollop of the zesty remoulade.