In a large bowl, combine goat meat, vinegar, and 1 tablespoon salt. Marinate in the refrigerator for about 1 hour. Rinse meat and drain well.
In a pot over medium heat, bring to a boil enough water to cover the meat. Add goat meat and boil for about 7 to 10 minutes or until scum begins to rise.
In a colander, drain goat meat. Rinse the meat and the pot.
In the clean pot, combine goat meat and about 6 cups of water. Bring to a boil, skimming scum that floats on top. When the broth has cleared, add onion, ginger, and fish sauce.
Lower heat, cover, and simmer for about 1 1/2 to 2 hours or until tender. With a slotted spoon, remove ginger and discard.
Wash tamarind and place in a pot with about 2 cups water. Bring to a boil and cook until soft and outer skins begin to burst. With a fork, mash tamarinds.
In a fine-mesh strainer set over a bowl, pour tamarind and liquid. Continue to mash with a fork, returning some of the liquid into the strainer once or twice, to fully extract the juice. Discard seeds and skins. Pour tamarind juice into the pot of meat.
Add chili peppers and continue to cook for about 4 to 5 minutes. Season with salt to taste.
Add green onions and cook for about 1 minute. Serve hot.