Buy some veggie stock. Or make it yourself. Whichever warm it up, throw in some slivers of fresh ginger and garlic. Some chunks of lemongrass if you have it, dried red chilies if desired. After simmering for 10 minutes or so, fish out those bits. Throw in some sliced mushrooms and a healthy dose of soy sauce. Pour into a bowl and garnish with chopped scallions.