Prepare your grill. Drizzle corn with 1 teaspoon oil, and season with salt and pepper; wrap in foil. Lightly coat the red onion slices with a bit of oil, and place corn and onion on the grill. Turn every 2 minutes for 10 minutes or until done.
Drizzle catfish fillets with oil, and season with salt and pepper. Grill for 4 minutes on each side or until cooked through. When finished grilling, remove the wrap from the corn, and carefully cut corn from the cob. Cut onion into small bite-size pieces.
In a small bowl, whisk together all ingredients for the dressing. Using a spiralizer, cut your zucchini using the smallest blade, and divide among four plates.
Top each with tomatoes, corn and red onion. Top with catfish fillet, and then drizzle with dressing.