If you have taken some type of psychology course you might be familiar with 'operand conditioning', which is the method developed by by B.F. Skinner in which  an association is made so that a certain stimuli produces a desired response.  Based on an association, we can get a turtle eating vegetables.  In Skinner's experiments animals were conditioned that when a certain light was turned on (stimuli), food would be suppllied (response).  At the end of the experiement the animals developed such an association that just by turning on the light, the animal would start to salivate.  Using Skinner's principles you can make your turtle associate the taste of a certain vegetable with that of something she really enjoys eating.

  Stimuli and response

It is not good to feed ground beef to a turtle, but this is an item that they really love and  it is easy to mix it with other products. I use ground beef (stimuli) in small amounts just to condition the turtle to develop a taste (response)  for vegetables so that she eats them with pleasure.  In my experiments I have used carrots.

  Procedure

I blend some slices of carrots and make a mixture of one part of carrots mixed with one part of ground beef.  I feed it to the turtle.  She will easily accept the mixture since it contains the 'meat flavor', but unconciously she will start to associate the taste of the carrots with that one of meat.
I feed this mixture a couple of days and then progressively I go on diminishing the amount of meat and increasing the percentage of carrots.
After one week of feeding the mixture, you can present the carrots alone to the turtle, cut up in small squares.  See if she eats them.  If she doesn't even touch them, continue feeding the mixture.  If she starts eating the carrots, you have succeded on the experiment.

  Note

The mixture is not intended to be fed to the animal as the only food source.  You have to continue to provide her with a varied diet while the experiment is in progress.