This recommendation is from Bakery Manis, where you will find tons of great Hawaii dining suggestions for vegan and vegan-friendly. See personal details of her Maui listings here.
This is a tiny little place that makes homemade kombucha and serves up a variety of lunch-worthy raw foods. According to Bakery Manis, "the kombucha was sweet and clean, not vinegar-y like some of the bottled stuff."
Location: 810 Kokomo Road #136, Haiku (At the back of Haiku Town Center)