Parashas Bo · Shemos 12:9 · TT note 7
Torah Temimah on Shemos 12:9, note 7 (on וּבָשֵׁל מְבֻשָּׁל) points to Pesachim 74a.
Sefaria — Exodus 12:9
Sefaria — Torah Temimah on Exodus 12:9
Sefaria — Pesachim 74a
E-Daf — Pesachim 74a
English: Rabbi Akiva says: That is a kind of cooking; rather, one hangs [the legs and innards] outside it.
Practical application of the ban on cooking: stuffing legs and innards inside would steam-cook them.
The legs and innards are hung outside the carcass for roasting, not placed inside where they would cook in their juices.