Superficial parotidectomy surgery is relatively uneventful post operatively. I suppose the surgeon told you not to have sour or spicy food for the first few days after the surgery. Now that it has been 20 days and the wound has healed it is ok to start back normal diet.. There is no need to have any food restrictions.. Also since it was low grade tumor, your doctor may have told you that no further treatment is required. However periodic follow up with examination and ultrasound scan should be done. In case of any further questions please feel free to consult online

There isnt any particular food that will cause this parotid tumor.As you have said you had it 20 years back and assuming you are not having any swelling at present.It is highly unlikely to reccur now, but not impossible. Usually mucoepidermoid low grade has a very good prognosis if the surgery is well done.