To make the raita, mix the yoghurt, mint and lime juice together in a bowl and season with a pinch of salt. Stir in the cucumber and radishes, cover and place in the fridge.
STEP 2
Preheat the grill to high and line a baking tray with kitchen foil.
STEP 3
In a small bowl, mix the garam masala, chilli and butter. Spread the spiced butter onto the mackerel and place on the baking tray. Grill for 1 minute, or until the butter melts and soaks into the fish.