Did you mean parsley, rather than lettuce? Parsley dipped in salt water is eaten as a rememberance of the salty tears shed by the Israelites (Though they weren't called that then) because of the hardships endured in Egypt.
Any lettuce can be eaten as long as it is thoroughly washed.
the jews eat onions
Yes.
Lamb can be kosher for Passover. However, Ashkenazi Jews traditionally do not eat lamb during Passover.
Some kosher restaurants are open for Passover.
Observant Jews see to it that everything they eat is kosher, pickles included.
There is the fast of the firstborn where firstborn males are supposed to fast the day of the eve of Passover. Once Passover starts, there is no fasting.
Rice (regardless of type) is classified as 'kitniyot'. This means that Ashkenazi Jews will not eat it during Passover but some Sephardi and Mizrachi groups will.
yes, they can. but no bread :(
Matzo, which is unleavened bread.
Jews eat the Passover meal to commemorate what happen to them a long time ago. In the Bible, it explains that the Jews were taken out of Egypt, in a hurry. Their bread did not have a chance to leaven, and so they ate what they call "matzoh" Now Jews have a meal with "matzoh" in it, to commemorate it.
The Jews eat the Passover Seder meal on the night of Passover (Pesach). It makes little difference whether Passover begins on Shabbat or on a weekday. Note that there are festive meals on every Shabbat, but they are not called "seder" and the foods are different.