The original Passover meal was not symbolic. The bitter herbs on the first seder plate were real bitter herbs, eaten in a real hurry on a real night. Targum Pseudo-Jonathan on Exodus 12:8 specifies the menu in exact terms: the flesh of the lamb, roasted with fire, eaten with horehound and lettuce, without leaven, on the night of the fifteenth of Nisan "until the dividing of the night."
Horehound and lettuce — marrubium and chasa — were two of the five species later listed in the Mishnah (Pesachim 2:6) as acceptable maror. The Targum's specificity reflects a tradition already in place by the time of the translation: Israel knew which plants the ancestors had actually eaten that night, and the rabbis preserved those names.
The phrase "until the dividing of the night" is striking. The Hebrew verse (Exodus 12:8) simply says the lamb must be eaten that night. The Targum gives a deadline: midnight. The paschal meal must be finished before the middle of the night, because the middle of the night is when the angel passed over. After that hour, the protection has already done its work; the meal belongs to the hours of suspense.
Roasted with fire, not boiled. Unleavened, not risen. Bitter, not sweet. Every feature of this meal refuses the comforts of a settled feast. It is food for people standing up to leave.
Takeaway: The seder plate was not invented later by the rabbis. It was prepared before dawn on the night that remade history.