For Pho Tom, first pour the soup into a pot, add the mushrooms, fish sauce and sugar and set aside.
Soak the noodles in boiled water while still hot for 5 minutes, then drain and divide among 4 bowls. Meanwhile, bring the soup to a boil with the mushrooms, add the shrimp and simmer for 2 minutes until cooked.
Divide the cucumber sticks among the noodles and ladle the hot soup with the mushrooms and shrimp over them. Serve Pho Tom.
Preparation Tip:
For a spicier Pho Tom, just add some chili.