Heat oil in a wok or pan and stir
fry garlic and onions for 30 seconds. Add chili sauce and sugar and
stir to make a smooth paste. Add stock or water, bring to the
boil, then add soy sauce and tamarind water or lime juice. Simmer for 1 minutes. The soup can be made in advance up
to this point. Bring soup back to a rolling boil
and add tofu, spinach, bean sprouts and tomatoes. Cook for about 2 minutes. Adjust seasoning and serve soup
piping hot, garnished with chopped basil leaves.