Wash spinach and cut into 2.5 in. length if too long.
Boil 8 cups of water and add 1 tsp of salt.
Add spinach and boil for 30 seconds.
Take spinach out and cool it down immediately with running water.
Once it's cooled down, squeeze with hands to drain any remaining water.
Mix sauce ingredients in a separate bowl. Add drained spinach. (Note: No need to squeeze lemon, just add the slice into a bowl).
Sprinkle some bonito flakes to finish.