In a medium-sized bowl, add all ingredients for pork balls, besides oil. Combine ingredients with your hands, making sure shallots and scallions are distributed throughout mixture.
Put a little oil on your fingers to help with pork sticking to your hands. Pinch off a small amount of pork, roll into a ball and set aside on a plate. Repeat with remaining mixture, which makes 12-15 balls; set aside.
Drizzle avocado oil in a large pot, over medium-high heat. Once oil is hot, add pork balls, being careful not to crowd the pan. Fry in batches, until balls are brown on all sides, turning once; about 5 minutes. Set aside.
In same pan, add ginger and shallots. Add more oil if pan is too dry after frying. Sauté until fragrant, about 2 minutes.
Add fish sauce and vinegar, stirring 1 minute.
Add stock, lemongrass and lime zest. Stir and bring to a simmer. Add pork balls. Cover, and let gently simmer about 10 minutes.
Uncover and bring to a boil. Add ramen noodles and boil
5 minutes.
Meanwhile, in a small bowl, whisk together sambal oelek and soy sauce. Add to pot, stirring gently. Remove lemongrass from pot and turn off heat.
Add watercress, stirring
gently, letting it wilt.
Serve noodles in shallow bowls, dividing equally and adding extra broth to the bowls. Top with cucumbers, sesame seeds and additional sprigs of watercress, if desired.