Put the ginger, garlic, peanut butter, soy sauce, lemon juice, and Sriracha into your blender or food processor. Blend until smooth, adding water by the tablespoon as needed to get things moving.
* How much water you use depends on two things: how thick you want your sauce and what sort of blender you're using. A high speed blender won't need as much liquid to get things going. For a thinner sauce (like a salad dressing), use more water. For thicker, back off on the water.