"uvashel": "bashel" (here refers to flesh that was) roasted (before, the understanding being that it is forbidden to cook it even if it had been roasted previously), as in (Devarim 16:7) "And you shall cook (i.e., roast) it and you shall eat it," and (II Chronicles 35:13) "And they cooked (i.e., roasted) the Pesach in fire as prescribed; and the holy (offerings) they cooked in pots, cauldrons, and pans, and they dispatched them to all the people." From here R.Yoshiyah said: If one takes a vow not to eat "mevushal," roasted (flesh) is (also) forbidden to him. "but roasted in fire": What is the intent of this? I might say: What is (more) fit for roasting should be roasted. It is, therefore, written "but (i.e., exclusively) roasted in fire,"
Uvashel Bashel Here Refers to Flesh That Was Roasted
Mekhilta Tractate Pischa 6:19