Place all vegetables, except tomatoes, into a large bowl with 3 tablespoons olive oil; toss gently to coat. Sprinkle vegetables with 1 tablespoon Basque Rub and season with sea salt, toss gently to coat. Set aside. Place ¾ cup of the tomatoes into a food processor and process until smooth. Set aside.
Heat plancha (flat cast-iron griddle) on grill over medium-high heat. Brush plancha lightly with additional olive oil. Place seasoned vegetables on the plancha and cook for 5 to 6 minutes or until nicely charred and tender-crisp, turning occasionally. Add the pureed tomatoes and remaining diced tomatoes to the vegetables and stir until heated through. Remove vegetables from plancha. Keep warm. Reduce heat to medium.
Season both sides of fish with remaining 1 tablespoon Basque Rub. Brush plancha lightly with more oil. Place fish on plancha. Cook fish on both sides until fish is lightly charred and flakes easily with a fork (about 10 minutes per 2.5cm thickness of fish).
Serve fish with plancha grilled vegetables and garnish with parsley.
This rub is also great on plancha grilled meats, burgers, vegetables, fish and poultry. See the recipe for Basque-Inspired Rub here