For the marinade:
Place the tamarind in a teacup or small bowl with 4 teaspoons of boiling water. Leave to soften for 20-25 minutes, mashing occasionally with the back of the spoon to extract all the flavour.
Push through a sieve with the back of a spoon into a bowl. Toast the cumin, coriander and fenugreek seeds in a dry skillet or frying pan.
Grind in a spice grinder or pestle and mortar. Mix with the prepared tamarind and all the other marinade ingredients.
To marinate the fish:
Spread the paste equally over both sides of all six tuna steaks. Cover and refrigerate for at least 2 hours or overnight won’t do any harm.
Give the tuna steaks enough time out of the fridge to lose their chill. Brush both sides of each steak lightly with vegetable oil and season well with salt and pepper.
Preheat the barbecue grill to high or ‘searing’ temperature. Clean and lightly oil the rack. The following timings are for a 3cm thick steak cooked pink. If thinner, adjust the grill time accordingly. Place the steaks on the grill and cook for 2 minutes. Do not attempt to move the fish until the flesh begins to mark and so release itself from, or if you like, burn itself off the grill bars. Use a fish slice to turn the steaks. Grill for a further 2 minutes on the flip side, or until well marked.
To serve, remove the crusted seared tuna steaks to a serving plate and surround with lime wedges. Serve with cucumber raita.
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