Heat up 1 tablespoon of olive oil in a large Dutch oven over medium high heat, then saute the onion for 3 minutes. Add the ginger, garlic, and lemongrass, and cook 2 minutes, stirring frequently with a bamboo spoon.
Reduce the heat to medium, then add the red curry paste and cook for 1 minute.
Add the chicken broth, coconut milk, tamari, fish sauce, brown sugar. Stir and bring to a gentle boil. Reduce heat to medium low and simmer uncovered for 15 minutes.
While it is simmering, boil the rice noodles for the lowest end of the cooking time, according to the package instructions. Drain well in a strainer and rinse with cold water.
Remove the soup from the heat, if the fat rises to the top, skim it if desired, then stir in the lime zest, lime juice and the chili paste.
When ready to serve, divide the noodles into each bowl and put ½ cup of shredded chicken. Ladle 1 cup of the hot Thai broth. Garnish with fresh cilantro, chopped green onions, lime wedges, and lime zest. If you want it spicy, add some sriracha sauce or chili flakes.