Place tuna, soy sauce and oil in a bowl, stirring well to combine. Cover and set aside.
Combine ½ tablespoon of yuzu and 1 teaspoon of the sugar in a bowl. Mix until sugar dissolves. Finely dice half the red onion and add to the yuzu mixture, along with the avocado. Stir to combine and season to taste.
Pour vegetable oil into a saucepan until one-third full. Heat over medium-high heat until 180°C. Thinly slice the remaining red onion, setting aside half for the salad. Deep-fry half the onion for 3- 4 minutes or until lightly golden. Drain on paper towel and sprinkle with shichimi togarashi.
Combine remaining yuzu and sugar in a bowl. Toss through mustard greens and set aside onion.
To serve, place 7cm high ring mould on a plate, spoon in half the tuna, top with half the avocado mixture and remove the mould. Sprinkle with fried red onion. Arrange salad, sesame seeds, nori and salmon roe around the outside of the plate.

MasterChef

Tuna & Avocado Timbale with Mustard Green Salad