Boil water in a large pot for the pasta and set aside.
Melt the butter in a large, heavy skillet or pan over medium heat and sauté the garlic, ginger and shallot until tender.
Add the curry powder and heat it through for a few minutes. Pour in the coconut milk and add the lemongrass, then bring to a gentle boil. Add the mussels, turn up the heat to high, cover with a lid and steam until the mussels open (this will take about 5 to 6 minutes). Discard any mussels that did not open. Using a slotted spoon, transfer the remaining mussels to a bowl and set them aside.
Add the tomatoes to the curry mixture and continue simmering until the tomatoes soften and the sauce thickens. Adjust with salt and pepper.
In the meantime, cook the pasta in generously salted boiling water according to the package instructions. Drain well, add to the curry and bring to a simmer. Add the mussels and stir gently to combine. Discard the lemongrass. Divide the curried noodles and mussels among individual bowls, sprinkle with the lime zest and top with the cilantro leaves. Serve with lime wedges.