"Nem ... van." ?
Nem and van are only substituted by nincs if they are beside each other. If another word/phrase separates them, they stay as they are. Here both "Nem a sütőben van" and "Nincs a sütőben" are correct translations.
"Nem a sütőben van" means "It is not in te oven" (therefore it is somewhere else). "Nincs a sütőben" means simply "It is not in the oven". The two sentences carry different meaning in Hungarian.
Indeed, I think a clearer and more direct translation of "nem a sütőben van" might be "It's not the oven that it is in."
I’m tempted to make a really dark alt-right-esque joke here.
There is a Hungarian word "közben" between the options.