Bring the water to almost a simmer over medium heat in a medium pot. Add in the konbu then lower the heat and let the konbu soak in the water for 30 minutes. Remove the konbu.
Turn up the heat to bring the water to a boil. Add in bonito flakes, dried shiitake mushrooms, ginger, salt, and shoyu. Simmer for 10 minutes to develop the flavor.
Strain the broth through a fine sieve or coffee filter and set the dashi broth aside.
Prepare the Noodles:
Bring a separate pot of water to a boil. Add saimin noodles and cook according to the package instructions (usually 1-2 minutes for fresh noodles).
Drain and rinse the noodles briefly under warm water to remove excess starch.
Cook the Toppings:
Spam or Char Siu: Slice and pan-fry Spam until crispy, or slice pre-cooked char siu.
Egg: Soft-boil, scramble, or fry an egg to your preference.
Green Onions & Kamaboko: Slice thinly for garnish.
Assemble:
Divide the cooked noodles into serving bowls.
Pour the hot broth over the noodles.
Top with Spam/char siu, kamaboko, green onions, egg, and nori (if using).
Serve hot and enjoy your homemade Hawaiian-style saimin!