1. Peel the lotus root skin, slice them 3 to 4 mm thick and add water and vinegar, then soak for about 10 mins.
2.Meanwhile making the filling , in a medium bowl, put together well drained canned tuna and onion. Pour into mayonnaise, sugar, salt and soy sauce. Mix well and set aside.
3. For the lotus root, gently pat them dry with a paper towel, then add salt and pepper both sides. On a slice of lotus root, place about 2 tbsp filling and spread. Cover another slice of lotus root on top and press down to make a sandwich! Repeat until you use all renkon and filling.
4. In a bowl, add egg and milk. Mix well. Coat renkon sandwich with flour thinly, then dip into egg-milk mix, and finally coat thoroughly with Panko (bread crumbs).
5. Put a tiny amount of panko to check the oil is ready. If it sizzles, it's ready! (or stick a chopstick in the oil and see if bubbles start to appear around the chopstick). Removing excess panko, press them gently. Fry them on both sides until browned.