Soften the vermicelli. Place the vermicelli in a large bowl. Pour room temperature water over the noodles and allow to soak while preparing the soup. (In room temperature water, the noodles should be tender in about 15 minutes. The goal is to get them about to that “al dente” point so that when you pour the hot soup over them, they will be tender but not mushy). Divide the noodles into 6 portions and place in individual serving bowls.
Toast the coconut. Toast the coconut flakes in a small, dry pan over medium heat, stirring or tossing them constantly to prevent burning. When the coconut is golden-brown, about 3 minutes, remove from heat, and set aside.
Make the soup. Pour broth in a large pot and bring to a boil. With heat at medium-high, add turmeric, chilli powder, garlic, and fresh chilli. Stir well. Add the chicken and continue boiling until chicken is cooked through (8-10 minutes). Reduce heat to a simmer and add fish sauce, ground peanuts, and coconut milk. Cook for 1 minute more and remove from heat. Add lime juice.
To serve, pour soup over prepared noodles. Top each serving with cilantro, spring onion, and toasted coconut.