Finely slice your purple onion, chilli, coriander stems, after which mince or grate your garlic. Add all of these substances to a medium-sized bowl. Add the zest of two complete limes together with all of the lime juice, sugar, fish sauce, honey, pinch of salt and pepper and toss effectively. Drain the vast majority of the olive oil from the tin of tuna and gently toss into the bowl, attempting to not break up the chunks into mush.