Soak the shiitake mushrooms in 3/4 cup hot water for 15 minutes until soft. Drain and reserve the water. Chop the mushrooms finely and set aside.

In a bowl, whisk together the black bean sauce and chili paste until well combined, and set aside.

Heat a wok and add vegetable oil. Add the chopped mushrooms and stir fry for a couple of minutes till they are slightly crisp. Add the ginger garlic paste and stir fry for another minute.

Pour the whisked sauce (black bean and chili paste) into the wok and cook for 2-3 minutes, stirring constantly. Add the firm tofu cubes and simmer for a minute or two, stirring gently.

Whisk cornstarch in 1/4 cup water (from the reserved mushroom water) and add to the wok. Mix gently and bring it to a boil until the sauce thickens slightly.

To assemble the lettuce cups, add two to three tablespoons mapo tofu mixture to each lettuce leaf and top generously with sliced green onions, sesame seeds, and roasted peanuts. Serve immediately for best flavor.