You can give him some veggies in the mornings and evenings but greys do not eat in "meals" like we do, they eat or snack all day long and some may munch during the night, be sure to have some pellets and a good seed mix in a bowl or separate bowls for anytime snacking.
When you offer vegetables try them different ways, raw, cooked, mashed, chopped, shredded and what ever other ways you can do them for some will like some certain ways and not others, do this for a while and you will find out what his favorites are.