Bring the 6 cups of water to a simmer in a pot. Add the sachets and let it simmer for 45 minutes, covered.

Heat 2 tbsp of sesame oil in a pan over medium heat. Add the thinly sliced onions and cook for 3 minutes. Add the garlic and ginger. Cook for another minute. Add the carrots and cabbage. In a bowl. mix together the chili flakes and 2 tbsp of sesame oil. Add this mixture to the pan and mix until well combined.

Cook just until the carrots and cabbage soften. Set aside.

Bring a of water to a boil and cook the noodles according to package instructions. Rinse well with cold water.

Combine the cooked spiced vegetable mixture with the broth. Taste for seasoning. Remove the sachets. Bring the soup to a simmer and add the seafood. Cook until the shrimp and cooked through and the mussels have opened up. Do not eat the mussels that do not open.

Add the hot soup to the noodles and serve.