Good looking dragon!
It looks like your feeding collard greens from the pictures. While they are slightly more nutritious, they are much less palatable and many dragons turn their nose up. If you want him to start eating veggies regularly, try some spring greens, yellow squash, or Romaine and you'll probably see a big difference in his veggie appetite. Once you get him regularly eating better tasting veggies, you can start working in the darker greens like collard, mustard, or turnip.