Although the Japanese drink several cups of green tea a day, it is rarely used in everyday cooking. However, adding brewed green tea to food recipes has a long tradition in some parts of China. For those who want to use as much green tea as possible, adding it to food can greatly increase one's daily intake. Also, the sweet yet astringent taste of green tea adds a subtle flavor to tea dishes that cannot be easily duplicated with any other ingredient. This is particularly true in mild soups where the unique qualities of green tea can be more easily experienced.
There are a few cookbooks that are entirely devoted to cooking with green tea. If you are interested, you might want to start with Cooking With Green Tea, by Ying Chang Compestine, a native of the People's Republic of China.