Preheat your oven to 400°F and toss the cubed sweet potatoes with a tiny drizzle of oil and a pinch of salt; roast for 20 minutes until tender and slightly caramelized.
In a small bowl, whisk together the smoked paprika, garlic powder, onion powder, cayenne, thyme, oregano, sea salt, and black pepper to create the blackening seasoning.
Pat the catfish fillets completely dry with a paper towel and press the spice blend firmly into both sides of the fish.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until it begins to shimmer.
Carefully place the catfish in the hot skillet and sear for 3 to 4 minutes per side until the crust is dark and the meat flakes easily with a fork.
During the last 2 minutes of cooking, add the chopped kale to the skillet with a splash of water, covering briefly to steam until bright green and tender.
Plate the blackened catfish alongside the roasted sweet potatoes and kale, finishing the dish with a bright squeeze of fresh lemon juice.