Submitted by Karen Klonoski of CT
Preheat oven to 400 degrees. Spray a 9X9 or 10X6 glass baking dish with non-stick spray.
Heat oil in skillet and saute mushrooms, onions and garlic for 3 min. over medium-high heat. Add spinach and cook for one minute, or until spinach is wilted. Remove from heat and drain liquid into the baking dish.
Add oregano to spinach and mushroom mixture and stir. Divide mixture evenly among sole fillets, and then roll each fillet carefully, placing seam side down into baking dish. Sprinkle with sherry, then top with shredded mozzarella cheese.
Bake 15-20 min.