Method:
Gently scrape out gills of mushrooms with a spoon. Slice caps into 4 strips each and place them in a large bowl. Combine peanut butter, vinegar, tamari, ginger, dates, garlic, serrano pepper and 1/3 cup water in a blender. Purée the mixture, adding more water a tablespoon at a time if necessary for it to blend smoothly. Reserve 1/3 cup of the sauce for serving and pour the remainder over the mushrooms. Toss and allow to sit at room temperature 1 hour for the mushrooms to soften.
Prepare a grill for medium-heat cooking or heat a grill pan. Thread mushrooms onto skewers. (If using wooden skewers, remember to soak them first.) Grill mushrooms, turning frequently, until tender and browned, about 8 minutes. Transfer to a platter and pour reserved peanut sauce over mushrooms. Sprinkle with cilantro and serve with lime wedges.