Heat olive oil in a large pot and saute the onion until wilted.

Wash and dry the tomatoes. Hold them from the stem end and grate by hand on a vertical cheese grater (with big holes). Add tomatoes to the onions and simmer for 10 minutes over low heat.

Meanwhile, rinse and drain the bulgur in a colander. Add to the pot. Pour in 6 cups of water, bring to a boil, reduce heat and simmer until bulgur is tender, about 15 minutes. Add more water, if necessary, to adjust the density of the soup. Season with salt and pepper and ladle into soup bowls. Add the tablespoon of strained yogurt to each of the bowls and serve.