Add dried shiitake and water to a bowl and set aside for a couple hours to rehydrate the shiitake. If you're short on time, use hot boiling water.
Squeeze the water out of the rehydrated shiitake and save the liquid in a separate bowl. Chop the shiitake and set aside with the other mushrooms.
To the bowl with the leftover shiitake liquid, add remaining seasonings (miso, sake, soy sauce, vegetarian oyster sauce, spicy doubanjiang, and sesame oil). Mix well and set aside.
Heat oil in a deep pan or wok over medium heat. Add garlic, ginger, and the white parts of the green onions. Once fragrant (about 30-60 seconds), add eggplant and mushrooms. Cook until the mushrooms have released their liquid and the eggplant is tender.
Add tofu and seasonings and stir thoroughly. It's OK if some of the tofu breaks apart.
Mix together cornstarch and 2 tbsp water to make a slurry. Once the sauce in the pan is boiling, add the cornstarch slurry and stir to incorporate. As soon as the sauce thickens, turn off the heat. Top with the green parts of the green onions. Sprinkle sansho on top if using and serve immediately.
Notes
GLUTEN-FREE: Use tamari instead of soy sauce, and check the ingredients for your doubanjiang and vegetarian oyster sauce since some contain wheat. You can use my homemade vegan oyster sauce.1) You can use other varieties of mushrooms depending on what's available to you. 2) Some mapo tofu recipes use soft/silken tofu. I prefer medium firm tofu since it has more of a bite to it but is still soft and bouncy. You can use silken tofu if you prefer, or a mix of both! 3) You can omit the vegetarian oyster sauce and add another 1-2 tsp of soy sauce.