“Was it after Noah that Hashem said that you can eat animals? Or after Adam and Chavah were expelled from Gan Eden?”
I think it was Noah (Bereishis 9:3).
However, the commentary in the Artscroll Talmud Bavli (Sanhedrin 56b) states: “Tosafos write that the Gemara below means that Adam was prohibited against slaughtering an animal to eat, but if an animal died on its own he could partake of it.”