If I was to solve a problem like this, it would be crucial to first understand why parents have been reluctant to volunteer for this duty in the past. Targeted solutions can only be had by knowing the cause of the lack of response.

For example, do parents not volunteer because they think they'll be (or actually will be) locked into every Monday, Tuesday, and/or Friday all year?
If so, designing a flexible schedule (and exactly what that means) may solve the problem.

Is the process for checking in and distributing the meals smooth and trouble-free or is it chaotic and in need of organization to make the task more pleasant for the volunteers? Have parents volunteered in the past just to arrive and find they aren't needed afterall? Are the cafeteria employees the volunteer needs to interact with helpful and pleasant?

How is this volunteer opportunity communicated to the parents? Is it in a format that most parents will see/read? Are multiple forms of communication used to reach parents? Are parents given plenty of advance notice or are the requests for help "last minute" (the day of, the day before, etc.)

Does lunch duty happen to occur when another, more popular, volunteering opportunity is happening (like recess duty, reading instruction, extracurricular coaching, etc.)?

Those are just a few questions off the top to start the process of determining why volunteers are few for this job. Hope this helps.

I need some suggestions on getting parent involvement when it comes to serving lunches at our school. We are a small school and we have lunches catered by Black Eyed Pea and on order to keep the cost down for parents we have to serve the lunches ourself. We only need help on Monday, Tuesday and Friday, but its hard every year to get volunteers!! HELP