Put the wood ear mushrooms into a heatproof bowl and cover them with boiling water. Set them aside as you complete the rest of the recipe, at least 20 minutes.
Thinly slice your pork belly into approximately 4-inch long strips. Heat a large Dutch oven over medium-high heat. Put the pork belly strips into the Dutch oven and cook, turning frequently, until the pieces are crispy, about 8 minutes total. Put the finished pieces on a paper towel-lined plate to drain, then put them in the warm oven with the tortillas. You will likely need to do this in two batches.
When the pork belly is finished cooking, drain the leftover grease from the pan, then return it to the heat. Add your sliced shiitake mushrooms and cook, stirring frequently, for 2 minutes. Add the coleslaw mix and one full recipe of the keto hoisin sauce and stir to combine. Using kitchen shears, thinly slice the wood ear mushrooms into the Dutch oven, then stir again and reduce the heat to low. Finally, use the same shears to slice the green onions, green parts only, into 1-inch strips. Put those into the Dutch oven, stir until they're just beginning to wilt, then remove the mixture from the heat.
To assemble the tacos, put two slices of pork belly on a taco, then top with some of the coleslaw mixture and drizzle with the leftover hoisin sauce. Serve immediately.
Macros per serving (2 tacos): 549 calories, 8 grams net carbs, 38 grams protein, 39 grams fat. The fat and calories may actually be lower, because the pork belly is cooked to remove more of the fat than usual.