Don't worry too much if your beardie won't eat salads yet, they not really important till their between a year and 2 years old. Most babies and juveniles won't eat greens and veggies, their like kids in that form
Just keep offering your beardie the salad and he/she will come around.
When I put my salad in it always consists of greens, some times lettuce (just as a treat now and then as it has no nutritional value), always collard greens and in the summer dandelion greens as well. On top of my greens is a veggie, either carrots or apples, then the fruit which varies from time to time between turnip, blue berries, strawberries and others.
Here is a great nutrition guide for beardies of what is good to feed and not good to feed.
http://www.beautifuldragons.com/Nutrition.html