In a large pot, combine the stock, squash, onion, ginger, fish sauce, salt, and Accent (if using). Bring to a boil over high heat. Lower the heat and simmer, without stirring, until the squash is tender, 5 to 10 minutes. Remove from the heat and stir in the curry powder. Let cool for at least 5 minutes, then stir in the cream. Ladle into bowls and garnish with the green onions and shallots.