I used huge tuna sashimi cuts from Banzai or Samurai because they are super thick. It was my first time making this based on interpretation from a lot of places I've been to. In the end, it turned out tasting just as good as the ones at the restaurant as my sister kept on eating and refused to let me finish with the presentation. The ponzu sauce has a sweet and tangy refreshing taste which complement the tuna, with added crunchy texture from sliced and fried onions. I would slice the onion thinner next time, even though the ponzu sauce gets rid of its raw taste and smell completely. Also add more colour to the presentation with chopped green onions. Anyways, here's the direction:
Sashimi grade Tuna strips
1/4 an onion
Ponzu sauce dressing:
2 tbsp. soy sauce
4 tbsp. rice vinegar
2 tsp. sugar
1. Sear strips of sashimi grade tuna with olive oil or sesame oil at medium heat just so that all the sides are cooked.
2. On a cutting board, slice tuna strips to no more than 1 cm thick.
3. Thinly slice the onion.
4. Mix all the ingredients for the dressing together
5. Plate the tuna topped with sliced onions, drizzle the dressing all over and garnish.
chopped up green onions
Wakame seaweed or nori
fried onions (optional) - adds extra flavour and crunch (I've seen it done at Guu gastown and absolutely love it).