I feel your pain. I have one bird that will sit hungry for days rather than eat anything fresh or any pellets. He only wants seed.
I read an article that said to get tiels to eat better, you should have 2 separate food dishes: one that stays in the cage all the time, and one that you only put in for a few hours a day. The one that stays in all the time has the food your bird doesn't care for. The one that you only put in for a few hours has a mix of what the bird is used to eating and the stuff he doesn't care for. I tried this technique to get him switched completely to pellets but it didn't work. To compromise, I measure a very small amount of the junk food, mix it with the same amount of pellets and leave that in all day. There is a second dish with just pellets in it that is always available. So he'll pick through and eat all the seed first... but at some point he does eat some of the pellets too.
I put fresh greens in a couple of times a week, but he doesn't even look at them. My vet suggested trying to make a puree with greens and sweet potatoes. It should be like a paste and you can roll little balls of it in their seed or pellets so that when they pick at those, they also get the healthy stuff. She said that sometimes they will even eat just that paste more readily than the whole greens... makes sense...but I haven't tried that yet.