Preheat oven to 220C/425F/Gas 7
Put all the ingredients in a bowl and whisk to combine. Set aside until ready to serve.
Put the prepared vegetables in a large baking tray, season with salt and pepper and sprinkle over the chopped garlic. Drizzle with the olive oil and combine so that the vegetables are evenly coated in the seasonings and the oil.
Put the baking tray in the hot oven and roast the vegetables, stirring once or twice, until they have charred a little and are done to your liking (10-15 min).
Heat the olive oil in a non-stick frying pan to a moderate heat and season the mackerel fillets with a little salt and some black pepper.
Fry the mackerel fillets on both sides , Two at a time if necessary, until they are nicely browned, cooked all the way through and the skin side is crispy (5-6 min). Leave in a warm place while you cook the rest of the mackerel.
Divide the roasted vegetables and the mackerel fillets onto two plates. Drizzle some of the Yogurt, Lemon & Mint Dressing over the vegetables, serving the rest on the side.
If liked, serve with some raw spinach sprinkled with chopped gherkin and spring onion.