A number of jungle lodges, such as Blancaneaux, have gardens to supply their own restaurants and many operate more or less organically. There also are a number of small herb and other kichen garden growers who sell in small quantities to restaurants.
Traditional Maya slash-and-burn agriculture was essentially organic and the subsistence farming practiced by Mayas in Belize today remains that way, out of necessity as much as anything (they can't afford expensive fertilizers and pesticides.)
By contrast, the Mennonites, who provide most of Belize's commercial agricultural production, generally rely heavily on chemicals.
I don't know of any true health food/organic stores in Belize, though it's possible there is something in Belize City.
There might be a market for such a business, selling to expats, vacationers and more health-conscious Belizeans (though Belize is the land of fried chicken, potato salad and Fanta). There are four or five areas in Belize that would be markets for this, but these areas are spread out all over the country -- Placencia, El Cayo, San Pedro, Caye Caulker, Belize City and Corozal Town. In a better world, Belize City would be the obvious place to locate, but with the crime situation there your profits would go to pay for armed guards.
--Lan Sluder www.belizefirst.com