In a large saute pan over high heat, add 2 tsp of oil, onions, carrots and celery. Once they are almost softened, add the garlic. Remove to a bowl and set aside.
Separate butter or bibb lettuce leaves, carefully wash and drain on paper towels.
Remove the stems and gills of 4 portobello mushrooms and slice lengthwise (keep them as wide as possible, but slice so they fit into the feed tube of the processor). Using the shredding blade attachment, process all of the mushrooms.
In the same large saute pan over high heat, add 1 tsp of oil. Saute the mushrooms adding the grill or burger seasoning, if desired. This is completely optional.
Meanwhile, whisk together the hoisin, rice wine vinegar, soy sauce and hot sauce. Add freshly grated ginger and red pepper flakes, if desired for extra heat and spice.
Fold together the vegetables and mushrooms with the sliced water chestnuts and divide the mixture between 6 lettuce cups.
Top with green onions and crispy rice noodles for garnish.