Peel the ginger with a spoon and grate it. Whisk it together with the remaining ingredients, or for a smooth dressing use a small blender or immersion blender to blend until creamy. (Or, make a double recipe in a standard blender.)
If the texture is very thick, stir in water a teaspoon at a time until it comes to the desired consistency. Serve immediately or refrigerate up to 10 days; allow to come to room temperature before serving and stir in a bit of water to loosen if necessary (it can become very thick during storage).