"Du hast ihn doch gekocht, oder?"
I also think I would be more appropriate to use in English, in this situation, "it" for the word "ihn".
Presumably because the noun for the thing you have cooked is masculine?
What happened to the "dock"? It isn't reflected in the translation.
This grimm grammer article is so good! Only through adding these particles can one really make the speech genuine-sounding. And the examples are "einfach total kool" ;)
It could also reflect the fate of a rooster who crowed too early in the morning once too often.