1. Preheat the grill, setting the burners to medium. Oil the grate.
2. In a bowl, combine the oil, lemon zest and juice, thyme, garlic and red pepper flakes. Season with salt. Set aside half of the marinade in a small bowl until ready to serve.
3. Add the fish to the bowl of remaining marinade and toss well to coat. Let marinate for 10 minutes.
4. Thread the tomatoes onto four metal or wooden skewers (which have been soaked in water for 30 minutes). Place on a plate. Brush lightly with oil. Season with salt and pepper.
5. Grill the tomatoes for 5 to 6 minutes or until slightly charred, turning them over halfway through cooking. At the same time, grill the fish for 2 minutes on each side or until the desired doneness (see chef’s tip).
6. Divide the spinach among four plates. Top with the fish and tomatoes. Drizzle with the reserved marinade.

Chef’s tip : Depending on the size and thickness of the halibut fillets, the cooking time may vary slightly. Instead of halibut, you can ask your fishmonger for a firm white-fleshed fish that will stand up well to the heat of the barbecue.