I also belong from an engineering background. MBA /PGDM is an integration of people sharing diversed educational background. Being an engineer you can choose any specialisation.
It's completely your passion about the subjects.
1)if you like to deal with people and guide them for professional benifit choose HR.
2) If you like to be the face of any project or you are an outgoing person believes in continuous challenges and performance oriented, opt marketing.
3) Good with reasoning and engineering background logics go for operations
4) Have patience to learn accounts and economics go for finance...
All the best!