Whether you're communicating in person or online, be sure to do the following:
Always, always, always frame requests positively. Point out how adding vegan options would make you and others more excited about eating at their establishments and how it would be a fun culinary experience for them. Do not criticize them for having no or few existing vegan options.
Restaurant owners want to know how offering vegan options will increase profits. Emphasize the increasing demand for vegan food and how meat consumption has declined 10 percent in the past seven years. Also note that by adding vegan options their restaurants will be promoted on sites like VegGuide.org and Happy Cow.
Remind the owner that when a group of people is deciding where to eat, if even one person in the group is veg, they will likely have "veto power" over where the group eats. So adding vegan options will bring in more than just new vegan customers.
Give examples of other businesses doing a great job of providing vegan options to show it is a growing trend.