Cook rice noodles according to package instructions. Once noodles are cooked, drain well and separate into serving bowls.
While the noodles are cooking, combine Thai Green Curry Powder with water and oil in a small bowl, and mix well into a thick paste. Adjust proportion of oil if needed.
Heat oil in a saucepan over medium fire. Add in garlic, scallions, and lemongrass (if using), and cook for 10-15 seconds, or until fragrant. Add in the Thai Green Curry Paste and continue to cook for another 10-15 seconds.
When everything is aromatic, pour in the broth and water, and bring to a boil. Add in the mushrooms and cook for about 1 minute until mushrooms begin to soften.
Add in tofu and zucchini, and continue cooking for 3-4 minutes, or until vegetables are just cooked. Add in sugar, salt, and generous squeezes of lime juice.
Stir well, have a taste, and then adjust any seasonings, if necessary. Ladle the soup and vegetables into the rice noodle bowls. Enjoy!