Warm a splash of neutral oil in a medium pot over medium heat.
Thinly slice half a medium onion and add it to the pot. Cook until soft, about 3-4 minutes.
Pour in 5-6 cups water and season with salt and fish sauce.
Bring it to a boil and cook for 3-5 minutes.
Add chopped greens and cook for 5 minutes until wilted.
Add finely chopped ginger and raw shrimp. Cook until shrimp is opaque.
Remove from heat and let rest for 5-10 minutes.
Taste and adjust seasoning if necessary.
Serve in individual soup bowls or a large bowl to share.
Optional tweaks: Substitute seafood with mild fish or ground pork/chicken. Add glass noodles to turn leftovers into a noodle soup.
