For the mix: Combine all the ingredients, except the sesame seeds, in a medium bowl. Add the dressing and toss gently to mix it all together. Add the sesame seeds and stir them through.
185 g canned tuna, 1 red capsicum, 1 lebanese cucumber, 3 celery sticks, 2 spring onions, 1 avocado, 1 tbsp sesame seeds, 1 tsp sesame oil, 1 tsp soy sauce, 1 tbsp kewpie mayonnaise, 1 tsp sriracha sauce