Add the julienned carrots and sliced serrano peppers to a jar and pour over a mixture of boiling water, rice wine vinegar, and salt. These will be ready for use once cooled and will get more pickled over time. The jar can be stored in the fridge for a long time.

Pat the tuna block dry before slicing into it. Cut down the block into strips, roughly 1/2 an inch wide. Then cut across the slices, making cubes. Toss into a bowl and set aside.

Add all seasoning sauce ingredients to a bowl and mix until homogenous. If using: add the wakame to a small bowl, and cover it with boiling water to rehydrate it. Once hydrated, remove it from the bowl and chop it up.

Combine the sauce in a bowl with all seasoned tuna ingredients so that everything is coated. Let marinate for a few minutes.

Optional: add warmed leftover rice to a bowl.

Add a sprinkle of furikake seasoning to create a little crunchy layer before adding the marinated tuna mixture over the top. Lastly, top with the spicy pickled carrot mixture and wakame seaweed. Enjoy!