Fish preparation: Remove scales, innards, both fillets, remove bones, and cut into 2×2 cubes with skin.
Thread all the fish cubes onto a skewer, pressing them tightly together. Season and cover with olive oil.
In a bowl, mix red onion, celery, and tomato finely diced. Season with lime juice, salt, finely chopped cilantro, and olive oil.
In a bowl, mix mayonnaise, soy sauce, and miso paste. Reserve in a pastry bag.
Cook the skewer on a hot grill for 5 minutes until easily detached. Turn the skewer and cook for another 3 minutes. Reserve on a tray and brush with olive oil again.