I would assume that if you’re lucky enough to be spending Mother’s Day with your mom, your plans probably include a meal more dignified than a burger and fries. But far be it from us to deny Mom, on her day, if she wants to gulp a milkshake in lieu of the traditional brunch. Z Burger in Tenleytown is more than happy to oblige such Mamas: the burger purveyor with a penchant for password-related promotion will be giving away free meals — consisting of a regular, cheese or veggie burger, a side of fries or onion rings, and a milkshake — to anyone who brings their mom to the location at 4321 Wisconsin Avenue NW location and recites the password “ThankZ Mom.” The deal’s on until 10 p.m. tonight.