1. Pound salt and white pepper in a mortar and pestle at a ratio of 60:40.
2. Season the tuna with salt and white pepper. Leave aside for about 20 minutes for the flesh to harden on a wire rack. Spray with oil.
3. Preheat a deep fryer to 120°C and heat a char-grill plate over high heat.
4. To make the garlic chips, add the milk and garlic to a small saucepan and slowly bring to the simmer. Once the milk comes to a simmer, drain garlic through a fine sieve and rinse with cold water. Dry on paper towel. Deep fry the garlic until lightly golden. Remove with a slotted spoon. Drain on paper towel and lightly season with salt.
5. Meanwhile, whisk the ground mustard with the hot water and vinegar, then add to a blender with the remaining white dressing ingredients. Process until pureed. Check the seasoning.
6. Lay a piece of daikon on a clean work surface, and spread over the snow pea sprouts and some mesclun along the closest side to you and roll up the daikon to form a roll. Cut into 2.5cm wide pieces. Repeat process to make 18 pieces.
7. Working quickly, seal the tuna on all sides on the char-grill plate, then plunge into an iced water bath. Pat the tuna dry with paper towel and place in the fridge for 10 minutes to rest.
8. Slice the tuna, from left to right on a 45° angle into 5mm-thick pieces, then roll up each to place on top of the daikon roll.9. To serve, fan 3 pieces of cucumber in the middle of the plate, place a daikon roll onto each, then a tuna tataki roll, then garlic chip on top. Spoon over dressing when serving.