In celebration of National Smoothie Day tomorrow, Jamba is offering fans a special one-day-only Mystery Smoothie. Wednesday only, fans can score a medium Mystery Smoothie for $5 by using the promo code âMYSTERY5â in the Jamba app or Jamba.com. Jamba also currently has a limited-time Golden Summer smoothie, available now through the end of June. The Golden Summer smoothie features a blend of pineapple juice, ginger puree, pineapples, mangos and peaches. Itâs available as part of Jambaâs Monthly Mystery menu via Jamba app or Jamba.com. National Smoothie Day is celebrated annually on June 21.