To make the kombu dashi, place the freshly boiled water in a medium saucepan and add the kombu and sea salt. Cover with a lid and leave to stand for 5 minutes.
Remove the kombu and place the pan over medium heat. Bring to a boil. (You can reuse the kombu, just store in an airtight container in the fridge or leave to dehydrate on a baking sheet).
Once boiling, reduce the heat to low and add the TVP to the saucepan. Allow to simmer for 2-3 minutes, stirring to make sure the TVP is all hydrated, then remove from the heat. Cover with a lid and leave to hydrate for 10 minutes.
While the TVP hydrates, combine the remaining ingredients in a medium bowl and set aside.
Once rehydrated, drain the TVP in a sieve and run it under cold water to cool it down. Transfer the hydrated TVP to a nut milk bag and squeeze out as much of the water as possible. While you squeeze out the moisture, the TVP should break apart quite easily. If it doesn't, place the drained TVP in a large bowl and use a fork to break it apart into small flakes.
Place the drained TVP flakes in the bowl with the rest of the vegan tuna salad ingredients and mix to combine. Season with salt and pepper if necessary before serving.