1. Preheat the side burner on your barbecue to MEDIUM/HIGH. Then take a frying pan and cover the bottom with a thin layer of olive oil. Then sauté the chopped onion, minced garlic, and diced green pepper.
2. Once they get a brighter color, add the aubergine, zucchini, and just one of the diced tomatoes. Season to taste and cook the vegetables until you see that the ingredients are soft but still firm on the outside.
3. Up next, grab the remaining tomatoes, grate, and add them to the pan. Then stir until everything gets combined (remove the skin from the tomatoes). Cook everything together for 3-4 minutes.
4. At the last minute, add the fresh thyme leaves and a fresh lemon wedge to the pan. Stir to integrate, letting it rest with the grill off for a couple more minutes, or it might burn and get a bitter taste.
5. For the final step, brush a grill pan with olive oil and when it is hot, add the mackerel fillets, cooking them for 2 minutes on each side. They cook very fast, so this is sufficient time.
Then simply plate up and enjoy!
