Upvote:3
In the context of the Turkish e-visa, the "return ticket" requirement is actually referring to the fact you have a ticket to leave Turkey. In general this would be referred to as a "return or onward" ticket, but clearly where you are reading they have only mentioned the "return" part.
What the Turkish Government is concerned about is the fact that you have a ticket to leave their country before your visa expires (and sufficient cash to sustain yourself for that period)
The fact you don't have a return ticket from the Schengen region isn't relevant as far as Turkey is concerned.