Preheat oven to 375 degrees. Remove stems from stuffing mushrooms and place in a shallow baking dish with lemon marinade for 20 minutes or longer. While mushrooms are marinating, place oil in a small saute pan on medium high heat. Add shallots and Portobello mushrooms and cook for 5 minutes, stirring frequently. Add tomatoes and spinach and cook for 3 minutes, stirring occasionally. Add remaining ingredients, except pine nuts and bread crumbs, mix well and remove from heat. Spoon a small amount of mixture into each mushroom, top with breadcrumbs and pine nuts, bake until mushrooms are slightly soft, approximately 10 minutes.