In a pressure cooker, add the bean sprouts, alfalfa sprouts, red cabbage, cucumber and yellow zucchini, along with half the amount of salt. Add the water and stir the contents. Pressure-cook until two whistles are done. Switch off the gas and open the lid after five minutes. Strain and reserve the liquid. Puree the solids and stir into the reserved warm liquid. Add the torn kaffir leaves to the liquid.
In a pan, add the oil. When it is warm, add the onions and rest of the salt. Simmer and cook until the onions turn golden and soft.
In a small bowl, take 3 tbsp of the soup and mix it with the sugar, tamarind and garlic pastes and cumin powder. Add this mixture to the onions and sauté continuously on a low flame, till all the water evaporates and the onions release the oil.
Remove the lime leaves from the reserved liquid and pour the liquid to the pan and stir. Bring this to a slow boil, stirring the soup occasionally.
While serving, garnish the soup with some fresh sprouts, lime leaves and roasted pumpkin seeds. Season with freshly ground black pepper.