In a blender or food processor, combine the tomatillos, garlic, green chile, cilantro and ½ cup water. Process to a coarse puree. Add the avocado and pulse until nearly smooth. Pour into a salsa dish. If necessary, thin to a drizzleable consistency with a little more water (I often add 1 to 2 tablespoons more). Taste and season with salt, usually about 1 teaspoon.