Sprinkle the cleaned mackerel with salt and black pepper. Place them in a lightly greased tray, cover with lemon slices and a little lemon juice and let sit for 20-odd minutes.
Heat a little oil in a pan and fry the onion and crushed garlic. Add the chopped into rings cleaned peppers and zucchini. Season them with salt and black pepper, add the cumin. Once the vegetables are lightly braised, put them into the tray with the mackerel and add 2/3 cup (150 ml) of hot water.
Put the dish to bake in a moderately heated oven until the fish are ready.