Preheat oven to 375 degrees Fahrenheit.

In a large skillet, heat oil over medium-high heat. Sauté onion until edges start to turn brown.

Add mushrooms and sauté until tender.

Add garlic and balsamic vinegar and let it reduce until almost all the liquid is absorbed. Set aside.

In a large mixing bowl, combine meat, bread crumbs, egg, garlic powder, salt and pepper.

On a piece of parchment, press meat mixture into a 12- by 18-inch rectangle.

Layer the mushroom mixture on top of the meat and roll like a jelly roll.

Cut into two loaves and pinch the ends.

Place loaves in a nine- by 13-inch baking pan and bake covered for 30–40 minutes or until the outside is slightly firm and the loaves are thoroughly cooked.

Heat oil over medium heat and sauté onion until slightly brown.

Add wine and cook for five minutes, or until liquid has reduced by about half.

Add soy sauce and the water-cornstarch mixture, and bring to a boil.

Add salt and pepper. Turn heat down and simmer for three to five minutes or until sauce thickens, stirring continuously.

This can be served as a whole meatloaf or slice and plate as an appetizer. Warm sauce separately and pour over right before serving.