Carefully clean the mushrooms with a damp paper towel and trim. Remove and chop the stems. Place the mushrooms caps, tops down, and the chopped stems in a 9x11" glass baking dish. Pour 1 tb olive oil and 1 tb sherry over the underside of each mushroom cap; pour the remaining olive oil and sherry over the stems. Cover and set aside to marinate at room temp for 1 hour. Mix together the marinade for the chicken and pour over the chicken slices. Cover and set aside to marinate at room temp for 1 hour. Grill the chicken quickly, about 1 to 2 minutes per side (they will be cooked further). Preheat the oven to 400~. Carefully spread 1 tb pesto over the underside of each mushroom cap. Sprinkle 1 1/2 ts sun-dried tomatoes on top of each pesto-covered mushroom. Evenly distribute the marinated mushroom stems on top of the tomatoes. Place 2 slices of chicken on top. Place the stuffed mushrooms in a greased 9x13 pan. Bake for approximately 20 to 25 minutes or until heated through. Serve immediately.