The vegie garden zone must be smaller in water volume then the rest. It sounds like when the lawn zones run they stay within the cut in and cut out adjustments on the pressure switch. When the small zone runs the pump puts out more water than the zone can use and cycles your pump.
I would recomend a pump tech have a look at it. You may have a water logged air tank or no tank at all. An air tank is highly reccomended. If this is not the case you may be able to adjust the pressure switch but I dought it if the pump cycles to kwikly. One other thing that may work for you is to size the vegie zone the same as your lawn zones by adding more sprinklers to it.
Good luck
Chuck

Have you tried using one zone at a time to see if it effects the pump?

Also my friends pump was doing what yours is doing and it turned out it was the air preasure tank at the top of the pump.
Some one had let some air out and this effected it.