This site is great for lists of good/bad veg
http://www.beautifuldragons.503xtreme.com/Nutrition.html
I feed mine spring greens as the staple, mixed with either watercress or rocket then i add a different variety each week e.g. butternut squash, apple, bell pepper, raspberries, tomatoe, cucumber...
Make sure you chop the pieces up finely. Dont worry about putting too much in, chances are he wont eat it all, maybe just a couple of munches- you can't overfeed salad
To get him to eat it, try handfeeding or putting the live food in his veg (or even wrapping veg around live food). Make sure the salad is colourful with smelly fruit/veg to entice him to it