Preheat broiler and line a baking sheet with foil.
Peel husks off tomatillos and place on the foil lined baking sheet with the jalapeno. Place in broiler and closely watch them until they get nice and charred on top. I can't give you a time for this because very broiler is SO different, but mine takes about 4-5 minutes.
Add the charred tomatillos to a food processor, remove the stem from the jalapeno and add that as well. Process or pulse until smooth with just a few chunks remaining. Pour into a bowl, add the onions, salt, water and lime juice and stir together. Place in the fridge until room temperature.
Add cilantro, green onions and avocado the the room temp salsa and stir together. Season with more salt to taste and add more water if it is too thick. Store in the fridge covered tightly for up to a week.