In a mixing bowl, combine ground pork, beaten egg, minced garlic, fish sauce, and breadcrumbs. Mix well and form into small meatballs.
Heat vegetable oil in a large pot over medium heat. Add chopped onion and cook until softened.
Add red curry paste to the pot and cook for another minute.
Pour in chicken broth and bring to a boil. Add the meatballs and cook until they float to the surface.
Reduce heat to a simmer and add coconut milk. Cook for another 10 minutes.
In a separate pot, cook rice noodles according to package instructions. Drain and set aside.
Add lime juice and soy sauce to the soup. Adjust seasoning to taste.
To serve, place a portion of rice noodles in a bowl and ladle the soup with meatballs over the top. Garnish with bean sprouts and chopped cilantro.