Buy tuna fillet that is the middle of the loin, free from the sinewy fat marbling as this is too chewy for ceviche or sashimi. Salsa criolla is a Peruvian salad in which the onions are soaked in salted iced water to remove the harsh taste and then tossed with fresh lime, chillies and coriander. It’s shockingly good with the raw tuna, scooped up with the crisp tortilla chips: this version is shown in the