Using a medium soup pot, saute onion and garlic in the olive oil until translucent, about 6 minutes. Pour in the chicken broth, and add the mushrooms, parsley, and salt and pepper. Cook at a gentle boil until the mushrooms are wilted, approximately 10 minutes. Add salt to taste.
Alternately, if you prefer a smoother soup you can puree the soup. To puree, use an immersion/ hand blender placed in the pot or fill a blender halfway each time, holding down the lid with a kitchen towel, and pureeing the soup until smooth, starting on low and increasing to high. A touch of milk (dairy or alternatives) can be blended into the pureed soup for a creamer consistency.
Serve topped with a small amount of Parmesan cheese and additional parsley for garnish.