Put the garlic and ginger into the container of an electric blender with 3 Tablespoons of water. Blend at high speed until you have a smooth paste. Set aside.
Pat dry the pieces of lamb. Heat the oil in a 2-quart pot over medium-high heat, and add the meat. Turn, and fry until the pieces are lightly browned on all sides. Remove with slotted spoon and set aside. Turn the heat off.
To the same pot, add the paste from the blender, the roasted and ground poppy seeds, the coriander, cumin, and turmeric. Turn the heat to medium, and fry, stirring occasionally, for about a minute. Turn heat to low.
Now add the browned meat and any juice that may have accumulated, the salt, cayenne, and black pepper. Stir and leave on low heat.
Combine chickpea flour and 4 tablespoons water in a bowl, mixing thoroughly until you have a smooth paste. Slowly add the chicken broth, stirring as you do so. Pour this mixture over the meat in the pot. Turn heat to high, and bring soup to the boil. Add uncooked rice if you are using it. Cover, lower heat, and simmer gently for half an hour or until the meat is tender. Stir in the lemon juice.
If you are using cooked rice, mix it into the soup just before serving. Pour the soup into a tureen or into individual bowls.
Mulligatawny soup can be served with both Indian and Western-style meals. Since it is thick and fairly filling, it can be a main course for lunch or light supper, followed by a green salad and fruit.