Turkey allows evisa facility for Indians with valid Schengen visas. I have a Schengen visa on my passport but it has expired. Does that still allow me to apply for evisa to Turkey ?
No, it explicitely says Valid visa, or variant on the e-visa page of Tr (https://www.evisa.gov.tr/en/prerequisites/). Therefore, I'd argue an expired Schengen visa won't work and you shouldn't attempt it.