If my dinner sales at a restaurant was doing good and our lunch sales are doing bad, what can I do to fix it?

Buy one/get one free might be a little over the top, but you should offer your dinner guests some kind of promotion if they come to lunch. Many restaurants run buy one get and identical or less expensive one for half price. You wouldn't have to do it forever, just a couple of weeks to see how it works out.

I just doubled lunch sales with a fax to our Chamber of Commerce members, it listed our signature items, and a the soup of the day and included 10% off for those who brought the fax in.

have a manager's blowout special for the lunch hours lol, seriously. have you ever seen a chinese restaurant menu and notice their lunch menu and how much cheaper the food is on the lunch menu. i suggest you put out a lunch menu.

Have a daily special. Or have one item on the menu that is fairly cheap for the lunch crowd like a meatloaf plate for $2.99 ( just an ex. since IDK what kinda prices you may have) Or, give your dinner crowd a coupon for, say, $2.00 off thier lunch check (bill)