zei is pronounced "zay," gezundt like the beginning of "gesundheit" when someone sneezes. The vowel is like the U in "push." Make sure it's a real "T" sound at the end, like "can't." My guess is that any Jewish person would get a kick out of it if you use it at the right moment!
Zei gezundt literally means "go in good health," but it really means...