Mix the coriander (the 30 g), chilli peppers, ginger and oil with a mortar to a paste. Spread thinly on both sides of the tuna and cover and leave to rest in the refrigerator for 1-2 hours.
For the salsa, peel and finely dice the mango. Mix with the onion rings, coriander and lime juice and cover and let rest for 20 minutes. Heat a cast iron pan (works best) and grease it lightly. Fry the tuna steaks on each side for 3-4 minutes. For a well-done steak, fry 2-3 minutes longer on each side. Serve with the salsa.