Cover mushrooms with hot water and let stand 1 hour. Drain; cut off stems. Rinse caps well; squeeze dry. Cut into 1/8-inch dice. Set aside.
Place tofu in large sieve. Bring 8 cups water to boil. Pour into metal bowl just larger than sieve. Place sieve gently in water. Let tofu soak 30 minutes.
Drain tofu. Mix mushrooms and preserved vegetable in medium bowl. Mix 5 tablespoons water and next 8 ingredients in small bowl.
Heat vegetable oil in wok or heavy large skillet over high heat 1 minute. Add green onions, garlic and ginger and stir-fry 1 minute. Add mushroom mixture and stir-fry 1 minute.
Stir broth mixture. Add to wok with peas and stir-fry until sauce boils, about 1 minute. Add tofu and toss gently to coat with sauce. Cook 2 1/2 minutes, tossing gently. Divide between plates. Sprinkle Szechwan powder over (recipe follows).
SZECHWAN PEPPERCORN POWDER: (Makes about 4 teaspoons) Heat heavy frying pan or wok over medium-low heat 1 minute. Add 1 tablespoon whole Szechwan peppercorns and stir until aromatic, about 4 minutes. Transfer to blender. Cool 10 minutes. Blend to a fine powder. Store at room temperature.