Which of these sentences sounds more natural?
1- We just cooked fish
2 - We just finished cooking fish
Usually I would use "We just made fish", but I want to use the verb cook. Which one should I use?
Most natural to me (British English) would be either
We've just cooked some fish.
We've just finished cooking some fish.
The only difference between them is that the second has emphasised the "finish" - that might imply that cooking the fish was a lengthy process, or perhaps that we have washed up the pans we were using.
I would not use "We just cooked" or "We just finished cooking", but I think that American speakers would do so.
And leaving out "some" is grammatical, but not natural, to my ear. I tend to use "fish" without a determiner when it has a general sense, (eg I often cook fish) but not when it refers to some particular fish.
And yes, I am saying that there is nothing to choose between your sentences, for naturalness.