In a small bowl, combine Cajun seasoning, paprika, garlic powder, onion powder, black pepper, thyme, and cayenne pepper if desired. Mix well and set aside.

Pat the catfish fillets dry with paper towels. Drizzle both sides with olive oil, then generously sprinkle the prepared seasoning mixture over the fish and massage it in.

Heat a skillet over medium-high heat and add olive oil and butter. Carefully place catfish fillets in the hot skillet and sear for 3-4 minutes on each side until blackened.

In the same skillet, reduce heat to medium, add a bit more butter, and sauté the minced garlic until fragrant. Add the diced tomatoes, simmer for 2-3 minutes.

Pour in the heavy cream, stirring until it thickens for about 3-4 minutes. Stir in the grated Parmesan cheese until melted.

Return the catfish to the skillet, spoon the sauce over it, and heat through for 2-3 minutes.

Transfer to plates and garnish with fresh parsley if desired.