Ceviche is a South American way of semi-cooking fish or meat by using acid from citrus fruit, and it’s essential you get good fresh fish. You can vary the fruit and fish but the results will be fresh, light and zinging with flavour.
Slice the fish into 1cm strips, put them in a bowl and pop them in the fridge. In a separate bowl or jam jar, mix the lemon juice, salt, chilli and garlic, then pop this in the fridge. Cut the top and bottom off the grapefruit, carefully peel away the skin, then separate them into segments and put these in a bowl, squeezing the juice from a few segments into the bowl.
When your guests are ready to eat, get the fish out of the fridge and combine it with the fennel, grapefruit and most of the mint leaves. Give the marinade in the bowl or jam jar a mix, then pour the juices over the fish mixture, delicately toss together and leave for 2½ minutes. Serve simply, on a big platter, with the remaining mint leaves and fennel tops sprinkled over, adding a little drizzle of olive oil and a few grinds of black pepper.