Make meatballs: Combine ground meat, 3 Tbsp fish sauce, and Sriracha in a medium bowl. Roll into small meatballs (about 2 rounded teaspoons each; you should have about 24 meatballs). Spread out on a small sheet pan or plate and refrigerate for 15 minutes while making the broth. (Refrigerating the meatballs will help them to hold their shape when added to the broth.)
Make broth: Using a rolling pin or meat tenderizer, smash the ginger, shallot, garlic, and lemongrass stalks just to open them up. (You want these aromatics to stay intact so that you can easily remove them later, but smashing them open will help them to release their flavors.) In a saucepan or Dutch oven, combine ginger, shallots, garlic, lemongrass, fish sauce, soy sauce, and stock. Bring to a simmer over medium heat. Simmer for 15 minutes.
Use a slotted spoon to remove aromatics from broth (you can discard them), leaving the broth at a simmer. Add meatballs to simmering broth and simmer until nearly cooked through, ~10 minutes.
When meatballs are nearly cooked through, add jasmine rice to soup and continue simmering until soup reaches your desired consistency, 5 minutes (for a more broth-y soup) or 15 minutes (for a consistency that is more like rice porridge / jok).
Remove soup from heat and stir in lime juice. Taste and add more fish sauce or soy sauce if you’d like the soup to be more salty.
Ladle into bowls and top with green onions and / or cilantro. Enjoy!