Preheat oven to 450°F. Combine okra, corn, onion, 2 teaspoons oil and 3/4 teaspoon Cajun (or Creole) seasoning in a large bowl. Spread the mixture out on a large rimmed baking sheet. Roast, stirring twice, until the vegetables are tender and beginning to brown, 20 to 25 minutes. Meanwhile, sprinkle both sides of catfish with the remaining 1 teaspoon Cajun (or Creole) seasoning. Heat the remaining 1 tablespoon oil in a large nonstick skillet over medium-high heat. Reduce heat to medium, add the fish and cook until just cooked through and starting to brown, about 4 minutes per side. Serve with the roasted vegetables.
