To make dressing, place the sesame seeds in a mortar and pestle and grind until fine and moist. Combine the soy sauce, rice vinegar, sugar, ginger, dashi granules and 1/2 cup water in a small saucepan and bring to the boil over high heat. Reduce the heat to medium and simmer, stirring, for 2 minutes or until the dashi granules have dissolved. Remove from the heat, cool.
Gradually combine with the ground sesame seeds, stirring to form a thick dressing.
Cook the noodles in a large saucepan of boiling water for 2 minutes or until tender. Drain, rinse under cold water and cool completely. Cut into 10cm lengths using scissors.
Place the snow peas in a large shallow bowl with the daikon, carrot, green onion, spinach leaves and noodles. Add the dressing and toss well to combine. Place in the fridge until ready to serve. Just before serving, sprinkle the top with toasted sesame seeds.