Adapted from Martha Stewart
In a food processor, pulse shrimp until finely chopped. In a large bowl, combine breadcrumbs, red-pepper flakes, and 1 teaspoon salt. Stir in milk and 1/2 teaspoon lemon zest. Fold in shrimp and chicken until just combined (do not overmix).
In a large pot, melt butter over medium. Add garlic and cook until fragrant, 30 seconds. Add broth soy sauce, fish sauce, and 2 cups water and bring to a rapid simmer.
Drop shrimp mixture by heaping tablespoons into broth. Cook meatballs at a gentle simmer until opaque throughout, about 5 minutes, turning halfway through. Divide pasta among four bowls and top with broth and meatballs. Combine remaining 1 1/2 teaspoons lemon zest with parsley and sprinkle over soup. Squeeze lemon wedges, take balls out of broth with a slotted spot, and serve.