We say ha lachma anya, and it is called that based on the pasuk (Devarim 16:3) which refers to matza by the term lechem oni. One famous answers (from Rabbi Akiva) is that we say (“onin”) upon this bread many things. Besides the straightforward meaning that we are reciting both Maggid and Hallel upon it, we can also understand this to mean that it is pretext bread. Thus, we see it is unusual and we ask (that is, mah haavodah hazot lachem or mah zot), and it becomes a reason for retelling the story of Pesach. Or, even better, we have many different explanations for why we eat it. The pasuk which gives the putative reason is for matzah for pesach dorot, and wouldn’t account for the matzah consumed in Egypt. And various reasons are given for it. And frankly, while there is presumably one true reason for eat, eat of the devarim harbeh which are given express and develop an interesting idea, all of which have value. So the devarim harbeh is a nice thing.
At a recent shiur in Rinat, a prominent modern Torah interpreter discussed what was meant by דִּי אֲכָלוּ אַבְהָתָנָא בְּאַרְעָא דְמִצְרָיִם, what matzah they ate at what point, and why. He developed the idea of matzah as the opposite of chametz, leavened bread, which was the Egyptian staple, and which even had a minister of bread (sar ha’ofim).
Along the way, he mocked the idea that the Egyptians were mean and therefore forced their Hebrew slaves to eat this bread of affliction. This, he said, was something kindergarten teachers taught the children in class, but lacks a basis in rabbinic literature.
Here is a basis, which appears in the Avudraham:
“And if you ask as to the meaning of ‘which our ancestors ate in Egypt’ since, after all, וַיֹּאפוּ אֶת הַבָּצֵק [Shemot 12:39] was only after they left Egypt; then, Rabbi Yehosef HaAzovi explains in the name of Ibn Ezra, who had been imprisoned in India, and they would feed him matza[-like] bread, and never gave him chametz. And the reason was that it was tough [heavy] and was not quickly digested like chametz, such that a little would suffice. And so did the Egyptians do to Israel.”
I agree that this explanation is not well supported by the Chumash text. But at the same time, there is some support in rabbinic literature for it. It is not purely an invention of the kindergarten morot.
Besides, even if we don’t find an explicit text to support it, the fact is that matzah is a word in the Hebrew language, and wasn’t invented on the spot. The Hebrews understood Moshe, and so it could make sense that it played some role in society, that some people would make unleavened bread for some purpose. And Ibn Ezra, with his personal experience, is engaging in realia, explaining what role it could play in some cultures. It is possible that the Hebrews made this bread for themselves for similar purpose, because it had to sustain them for a tough day of work. And then we can understand the pasuk of it being lechem oni, bread of affliction, that is bread that they ate in Egypt regularly, during their affliction. And then it is not without some scriptural tie-in.
I’ll close with another possible explanation of lechem oni I came up with. Maybe it is obvious, or maybe it is my own chiddush. The process of making the bread, and the experience of eating a bread of this texture, parallels that of affliction. With chametz, you put in yeast and allow the bread to expand, and you end up with a light, fluffy texture. But in Egypt, there was lachatz, oppression, in which the Hebrews were suppressed and not allowed ease and breathing space. And so too, we do not allow the dough to become chametz and the result is a bread which has been afflicted and has an afflicted texture.