1Chop red onions, slice chives and Thai chilies, and grate some ginger.
2Thinly slice some radishes using a mandoline and place them in ice water to keep them crunchy and prevent oxidation.
3For the coconut sauce, combine coconut milk, fish sauce, salt, sugar, halved Thai chilies, and grated ginger in a pot. Simmer on low heat for a few minutes, then add calamansi juice and chill in the fridge.
4Slice the yellowtail tuna into sashimi-style pieces.
5For the marinade, combine coconut or cane vinegar with salt, sugar, red onion, grated ginger, Thai chilies, chives, calamansi juice, and olive oil. Mix well.
6Marinate the fish for about five minutes.
7Pour some chilled coconut sauce into the middle of a plate. Arrange the marinated fish around the edges.
8Add some red onions, Thai chilies, and chives from the marinade on top of the fish.
9Garnish with radishes and cilantro. Drizzle with olive oil.