This room-temperature soup is inspired by the California avocado groves.
Place the scallions and cilantro in blender, and blend until smooth. Add the lime juice, tomatillos, and cucumbers; blend until smooth. Peel the avocados, remove pits, and cut into large chunks. Transfer to blender. Add the stock, salt, pepper, and Tabasco; blend until smooth, stopping to scrape down the sides once or twice. Taste for seasoning. Transfer the soup to a nonreactive container. Cover with plastic wrap, pressing down so plastic touches soup. Let chill 1 to 2 hours (do not keep overnight).
Mix well before serving, and adjust the seasoning to taste. Slice the baguette crosswise into quarter-inch slices, and lightly toast the slices. Ladle the soup into bowls. Top each serving with half a tomatillo and a dab of creme fraiche. Serve with a slice of toast and a lime wedge.
Homemade chicken stock is preferable in this recipe, since the flavors of the soup are so delicate.
Homemade chicken stock can be replaced with canned low-sodium chicken stock. Creme fraiche can be replaced with sour cream.