Step 1

Cook onion: Heat oil in a cast iron skillet over medium-high heat. Add onion, sauté until softened, about 3 minutes.

Step 2

Add other veggies: Add mushrooms, sauté, stirring frequently, for 5 minutes. Add carrots and celery, sauté until the mushrooms are golden brown and carrots are tender, about 5 minutes.

Step 3

Add seasonings: Reduce heat to medium. Add garlic and ginger. Cook, stirring frequently, until fragrant, about 1 minute. Add tamari, rice vinegar, and sriracha. Toss to coat.

Step 4

Finish cooking: Stir in bamboo shoots, water chestnuts, and sesame oil. Cook until warmed through, 3 to 5 minutes. Stir in green onions and remove from heat.

Step 5

Serve: Transfer the lettuce wrap filling to a serving bowl. Scoop some of the filling into a lettuce leaf ("cup"), sprinkle with cashews and other toppings of your choice.