Prepare the broth. Add shrimp shells, vegetable broth and coconut cream to a 2-quart saucier and bring to a light boil over medium-high heat. Reduce heat to very low and keep warm until ready to use.
Prepare the curry mixture. In a 3.5-quart sauté pan (or sautuese), melt the butter over medium heat. Add onion, celery, and chilies. Cook, stirring occasionally until softened, about 5 minutes. Add garlic, ginger, and curry paste. Cook, stirring often, until fragrant, about a minute. Stir in flour and cook for an additional minute.
Pour the stock and coconut milk, a little at a time, through a mesh strainer to remove the shrimp shells, into the curry mixture, stirring to combine. Once the broth and coconut milk are completely incorporated, add the potato. Raise the heat to medium-high and bring to the boil. Then reduce the heat to medium-low, cover, and simmer, stirring occasionally, for 15 minutes or until potatoes are just tender.
Prepare the bok choy. Heat an 11-inch skillet medium-high heat. Add the avocado and sesame oil. Once the oil is hot, add the bok choy and turn the heat down to medium. Toss to coat with the oil. Add the water and cover to steam. Let steam for about 2 minutes or until the bok choy is tender but still a little bit crunchy.
Add the mussels and shrimp. Raise the heat of the curry to medium-high, add the mussels and cover the pan. Cook for 2 minutes, then add the shrimp and cook until the shrimp are opaque, and the mussels have opened, about 2 to 3 minutes more. Discard any mussels that do not open. Stir in the cilantro and lime juice.
To serve, place a portion of rice, and bok choy in a low sided bowl, then spoon over shrimp, mussels, and the curry mixture. Sprinkle with green onions, more cilantro (optional), a lime wedge (optional) and serve with warm naan.