This recipe is dedicated to the mushroom lovers. Since it can be modified for both seafood lovers and vegetarians, this makes for a really fast and fancy appetizer at a formal dinner party. Portobello mushrooms stuffed with red onion, fresh spinach, roasted red peppers and garlic, shrimp or artichokes, topped with mozzarella and glazed with a balsamic reduction. Beautiful presentation that is sure to impress.