Line a saute pan with foil and place it over medium heat. Husk and wash the tomatillos and place them in the pan to roast. Add the Anaheim chile. Using tongs, continue to turn them to brown them on different sides until they start to soften, about 15 minutes. The tomatillos should have brown spots on several sides and be a little soft; the chile should be browned and fairly soft. Remove and let cool enough to handle. Core the tomatillos and place in the bowl of a food processor. Core and seed the chile, and place it in the same bowl.
Add one of the avocados and all of the rest of the ingredients to the same bowl and process until fairly smooth.
Chill for 2 hours. To serve, cut the other avocado into cubes and add it to the soup.
Garnish with a couple of sautéed shrimp if desired.