1.For lotus root crisps, combine vinegar and 250ml water in a bowl. Submerge lotus root in water and leave to soak (10 minutes). Drain and dry well with paper towel.
2.Heat oil in a saucepan to 170°C. Fry lotus root, in batches, turning occasionally, until golden (3 minutes); drain on paper towel. Sprinkle with shichimi togarashi and ½ tsp sea salt flakes.
3.For ota ika, combine tuna, shallot, fish sauce and lime juice in a bowl, season to taste, and marinate for 5 minutes. Stir in coconut milk and half the chilli; refrigerate until fish turns opaque (10 minutes).
4.Arrange tuna on serving plate with cucumber, nashi pear, remaining chilli, nasturtium and lime zest. Serve with lotus root crisps and blood lime.
Note: If fresh lotus root is unavailable, substitute sliced frozen lotus root, available from Asian grocers and specialty food shops.