Pour the broth into a pot. Add the onion, garlic and tomatoes. Sprinkle in some salt and pepper.
Set the stove to medium-low and heat the broth slowly until simmering and the vegetables soften a bit.
Stir in the tamarind paste. Taste and add more salt and pepper, if needed.
Add the Chinese broccoli, pushing them down gently into the broth. Simmer for another seven to ten minutes.
Serve the Chinese broccoli and tamarind soup immediately.