Blister the tomatillos directly over a gas flame or under the broiler, using a pair of tongs. When the tomatillos are charred all over, add them to a blender. Add the olive oil, garlic, lime juice, avocado, jalapeno and onion to the blender. Pulse until the tomatillos break down. Season with salt and pepper. Serve immediately, garnished with chopped parsley.