1) Make a marinade for the tuna by blitzing the coriander, garlic spices and lemon juice together. Add the oil slowly until it thickens.
2) Pour 2/3 of the sauce over the tuna then cover with cling film and marinate for at least 20 minutes but not more than 4 hours.
3) Heat a griddle pan or frying pan and cook the tuna for 2 – 4 minutes for medium rare adding 2 more minutes for well done. Turn once.
4) Serve with the remaining marinade poured over.