Add the leftover lamb bone to the water with the thyme, simmer until the meat is soft and starts to fall off the bone. Strain all the stock off and return to the saucepan.
Add the vegetables to the stock that is at a simmer. While the vegetables are cooking sort through the meat removing any gristle or similar. Dice the meat and return to the soup.
When the vegetables are cooked through check the seasoning and adjust with salt and pepper then serve.