Combine the smoked paprika, garlic powder, onion powder, thyme, oregano, cayenne, sea salt, and black pepper in a small bowl.
Pat the catfish fillets dry with a paper towel and coat both sides evenly with the prepared Cajun spice blend.
Heat the avocado oil in a cast-iron skillet over medium-high heat until it begins to shimmer.
Place the catfish in the hot skillet and sear for 3 to 4 minutes per side until the crust is dark and the fish is opaque.
While the fish rests, melt the butter in a small saucepan over low heat and stir in the lemon juice and parsley.
Add the sliced zucchini to the skillet and sauté for 2 minutes until tender-crisp, absorbing the flavorful pan drippings.
Serve the blackened catfish over the zucchini and drizzle with the velvety lemon-herb butter.