if time allowed

  וַיֹּאפ֨וּ אֶת־הַבָּצֵ֜ק אֲשֶׁ֨ר הוֹצִ֧יאוּ מִמִּצְרַ֛יִם עֻגֹ֥ת מַצּ֖וֹת כִּ֣י לֹ֣א חָמֵ֑ץ כִּֽי־גֹרְשׁ֣וּ מִמִּצְרַ֗יִם וְלֹ֤א יָֽכְלוּ֙ לְהִתְמַהְמֵ֔הַּ וְגַם־צֵדָ֖ה לֹא־עָשׂ֥וּ לָהֶֽם

We read in the haggadah "Matzah zu she'anu ochlim al shum mah?" and the haggadah goes on to answer, as seems to be pshat in our pasuk (12:39), that the Egyptians were in such a rush to kick us out that they did not even give us time to bake bread for the road.

The Ran in Pesachim (25b in pages of RIF) infers a big chiddush from this statement.  The implication of the haggadah and of the pasuk is that had we had time, we could have baked bread even though it was Pesach -- no problem of bal yera'ah!   

Ramban explains the pasuk differently to avoid this conclusion:  

וטעם ויאפו את הבצק – שאפו אותו מצות מפני המצוה שנצטוו: שאור לא ימצא בבתיכם כי כל אוכל מחמצת ונכרתה

ואמר כי גורשו ממצרים – לומר שאפו אותו בדרך בעבור כי גורשו ממצרים ולא יכלו להתמהמה לאפות אותו בעיר, ולשאת אותו אפוי מצות, ועל כן נשאו אותו בצק ומשארותם צרורות בשמלותם על שכמם (שמות י״ב:ל״ד), ומהרו ואפו אותו טרם יחמץ בדרך או בסכות, כשבאו שם לשעה קלה כדברי רבותינו.

The pasuk speaks about the dough אֲשֶׁ֨ר הוֹצִ֧יאוּ מִמִּצְרַ֛יִם, which they took out of Egypt and baked into matzah on the road.  According to Ramban, two things the require explanation: 1) why they were eating matzah and not bread; 2) why they had to bake it on the road and not at home.  The answer to the first question, the pasul tells is,  is that כִּ֣י לֹ֣א חָמֵ֑ץ, because Hashem had prohibited chametz and commanded Bnei Yisrael to eat matzah.  The answer to the second question is that the Egyptians rushed them out, כִּֽי־גֹרְשׁ֣וּ מִמִּצְרַ֗יִם וְלֹ֤א יָֽכְלוּ֙ לְהִתְמַהְמֵ֔הַּ.  

The difficulty with the Ran (as the Tzlach points out) is that the Mishna (Pesachim 95) lists the differences between Pesach Mitzrayim and Pesach as celebrated in future years and absent from that list is the Ran's assumption that there was no prohibition of bal yera'eh on that first Pesach in Egypt.

The difficulty with Ramban is that the pshat may work well for the pasuk, but it does not fit the haggadah so well. "Matzah zu...al shum mah" sounds like we are offering an explanation for why we eat matzah, not just for why it was baked it on the road.