I like to offer veggies in the morning. I will remove dry food bowls and put in the fresh breakfast. Leave for 15-20 minutes. If they don´t eat, swap the bowls back. Do this daily.
Offering variety is good. So, different veggies, presented in different ways. Maybe mashed, or processed, or chopped finely, or chopped in chunks. Some like large pieces on skewers.
A good tip is to sprinkle with millet or quinoa. I also like to bury one or two sunflower seeds in there for my picky eaters.
You may end up wasting a lot, so only offer a couple of teaspoons worth of veggies until he starts eating them.
You can also sit and eat next to the cage. Sit and eat some veggies, then offer it to him.
This is a great link:
My Chop "Recipe"
Lot´s of help with whch foods to use, and how to store it when you make bulk, and also more tips