Heat a drizzle of oil in a large nonstick frying pan over medium-high until shimmering. Add mushrooms and cook, tossing often, until golden brown all over.
Add shallots, garlic, and ginger to the pan. Cook, stirring often, until aromatics are softened and fragrant.
Remove pan from heat; season mushroom mixture lightly with salt and pepper. Mix in spring onions, chillies, mint, soy sauce and half of the peanuts.
Transfer larb (mushroom mix) to a platter or large bowl. Serve in lettuce cups with remaining peanuts alongside and wedges of fresh lime.