In a large bowl, soak noodles in room temperature water for 30 minutes for small or 60 minutes for medium noodles.
Bring a large pot of water to boil to blanch noodles just before serving.
In a dutch oven on medium heat, add oil, curry paste, sugar and ¼ cup coconut milk and stir. Cook until most of the moisture has evaporated and the paste is frying in the oil.
Add chicken and cook until pieces are separated. Then add chicken broth and lime leaves. Bring to a simmer and let it simmer for 3-5 minutes until chicken is completely cooked through.
Stir in remaining coconut milk and heat through. Taste the curry, to see if it needs more fish sauce or sugar. Adjust to taste.
Turn down the heat, add tomatoes and cook for another minute.
Blanch noodles 5 seconds for small or 8-10 seconds for medium and place noodles in individual serving bowls. Ladle soup over the noodles.
Garnish with cucumbers, bean sprouts and cilantro.