Preheat oven to 400°F and line a baking sheet with parchment paper.
Toss the broccoli and bell peppers with 0.25 tbsp of olive oil, 0.125 tsp of sea salt, and 0.125 tsp of black pepper.
Spread the vegetables in a single layer and roast for 15-18 minutes until tender and slightly charred.
In a small bowl, whisk together the smoked paprika, garlic powder, onion powder, dried thyme, dried oregano, cayenne pepper, remaining sea salt, and remaining black pepper.
Pat the catfish fillets dry with paper towels and coat both sides evenly with the prepared blackening spice mixture.
Heat the remaining 0.25 tbsp of olive oil in a large cast-iron or non-stick skillet over medium-high heat.
Sear the catfish for 3-4 minutes per side until the spice crust is dark and the fish is opaque and flakes easily.
Plate the blackened catfish alongside the roasted vegetables and serve with a fresh squeeze of lemon.