Smash up the chilli and the coriander seeds in a pestle and mortar. Peel and chop the garlic, pick and finely chop the herb leaves and add it all to the pestle and mortar with a drizzle of oil and lemon juice, to taste. Mix together, and season with sea salt and black pepper. Lay out your tuna steaks on a tray, season both sides and rub all over with the herb mixture. There are two nice ways to cook it: I prefer to cook it on a griddle pan or in a frying pan. Your pan should be very, very hot. Put in the tuna and what you want to do is sear it so that it toasts, fries and browns (about 45 to 60 seconds on each side). Once cooked, I like to rip the steaks in half and serve with salad and chips or boiled potatoes and a big wedge of lemon. It’s quite sexy sometimes with some marinated sun-dried tomatoes, olives, basil… The possibilities are endless.