Prepare the shirataki noodles by rinsing them thoroughly under cold water and patting them dry with a paper towel.
Cut the napa cabbage into 2-inch wide pieces, remove the stems from the shiitake mushrooms, and slice the tofu into 1-inch cubes.
In a small mixing bowl, whisk together the dashi broth, tamari, mirin, and coconut sugar until the sugar is dissolved.
Heat the avocado oil in a shallow cast-iron pot or heavy-bottomed skillet over medium-high heat.
Sear the thinly sliced beef in the hot oil for about 1 minute until just browned, then push the meat to one side of the pot.
Arrange the cabbage, mushrooms, tofu, and shirataki noodles in separate clusters in the pot.
Pour the tamari-dashi sauce over all the ingredients and bring to a gentle simmer.
Reduce the heat to medium-low and cook for 5-7 minutes until the vegetables are tender and the tofu has absorbed the broth.
Garnish with sliced green onions and serve immediately with a fresh cracked egg on the side for dipping or poaching directly in the hot broth.