Preparation / Directions:
Preheat oven to 325F.
Combine the oyster sauce, hoisin sauce, ketchup and serrano chili. Let the mixture sit for several minutes to let the serrano flavor the sauce. This step may be done well ahead.
Make sure the stems are completely cut off the mushroom caps. Paint the caps with a little oil and a little of the sauce. Place them on a baking sheet and bake in the preheated oven for 2 minutes.
While the caps are baking, roll the oysters in the rest of the sauce so that they are evenly coated. Remove the caps from the oven and place an oyster on each cap. Return them to the oven for about 6 minutes. Remove and place on serving dishes and serve immediately.
Note: Yeah, I know, it's NOT BBQ, but it's too damned good to pass up. Besides, I wanted to see if you were paying attention.
Editor: this works on a cover grill just fine and gives the end-product a nice smoky tast