Today is National Rotisserie Chicken Day. Never heard of it? That's because it's being declared for the first time ever, thanks to Boston Market.The restaurant petitioned the National Day Calendar to "declare a day in honor of the healthful cooking method." And that day is June 2.To celebrate -- because what good is a day without a deal -- Boston Market is offering a free third regular side dish with the purchase of any rotisserie chicken individual meal.To snag that extra side of macaroni and cheese, you'll need a coupon. Get it here.