“a person (fish) ideally suited to another (food) as a close friend or romantic partner (it goes well on a dish together).”
Despite it’s name, Lemon sole isn’t actually a sole, it’s a flounder, and it doesn’t taste of lemons. So whoever called it a lemon sole in the first place has a lot to answer for. Imagine calling a chocolate bar a chocolate bar, and it wasn’t a chocolate bar at all, it was a pickled onion.
Lemon sole is, though, a beautiful tasting flatfish, not really related to the Dover sole (they’ve got different Latin family names). Prominent in European waters, they have a lovely texture and mild taste, meaning they’re well suited just with simple ingredients so as not to overpower it.