Cook the rice noodles according to the package directions.
Meanwhile, heat the oil in a large pot over medium heat. Add the scallions and curry paste. Cook, stirring often, until the scallions are tender, 6 to 8 minutes.
Add the coconut milk, fish sauce, and 2 cups water and bring to a boil.
Add the fish. Reduce heat and simmer until the fish is opaque throughout, 2 to 4 minutes.
Serve over the rice noodles, topped with the cabbage, chilies, and lime wedges.