1. For the Soup, place all ingredients in blender container; cover. Blend on high speed until smooth. Remove insert from blender cover. With blender on, gradually add enough water (1 to 1 1/2 cups) until soup is a drinkable consistency.
2. For the Topping, heat oil in medium nonstick skillet on medium heat. Add remaining ingredients; cook 5 to 7 minutes or until mushrooms begin to brown and pistachios are toasted, stirring occasionally.
3. Pour soup into beverage glasses. Top each with 1 tablespoon of the Topping.
Make Ahead: Prepare soup and topping as directed. Cover and refrigerate up to 3 days. To warm soup and topping, place in microwavable mug. Microwave on HIGH 30 seconds to 1 minute or until heated through.