Heat oil in a large stockpot. Add curry paste, garlic and ginger, and cook 2 minutes. Stir in diced sweet potato. Add bok choy stalks and broth. Bring to a boil; reduce heat and let simmer 5-7 minutes, or until sweet potatoes are tender.
While the soup is cooking, cook noodles according
to package directions. Once the sweet potatoes are tender, stir in coconut milk, fish sauce, and agave. Stir in greens of bok choy,
and let cook for about 5 minutes to wilt, stirring occasionally.
Drain noodles and divide evenly among four bowls. Serve
soup and vegetables over noodles; top
with red onion, cilantro, a wedge or two of lime, and
a drizzle of hot sauce, if desired.