I've never heard of sinigang na litson until I visited one (supposedly) famous Kapampangan restaurant (Bale Dutung) in Angeles City, Pampanga in the Philippines just last month, but it's actually pretty tasty. This is also a great way to use your left overs.
Fresh tamarind (about 10 - 12 pieces depending on size). Instant sinigang mix may also be used.
1 md onion (diced)
2 tomatoes (diced)
Medium sized Radish (cut in cubes)
1 cup sitaw (cut in 4" pieces)
2 cup young Kangkong leaves (water spinach)
2 pcs long green pepper
4 cups of water.
Salt (or Patis) to taste
In a stew pot, boil the water. Add the tamarind until they are tender. Take the tamarind out of the water and use a strainer to collect the juice taking out all the skin and seeds out. Add the tamarind extract, tomatoes, radish, and onion in the same water. When the radish is tender, add the litson and sitaw and let simmer for another 2-3 minutes. Finally, add some salt to taste and place the pepper (first) and kangkong on top. Cover and simmer for about 2 minutes. Serve with white rice.
Note: If you can't find kangkong leaves, spinach is a great alternative. Personally, I use fresh tamarind (if available) because I don't like all the extra ingredients included in the instant sinigang mix.