Is a seed mix better than pellet? To my way of thinking, yes, provided that it does not contain any thing other than seeds. Once they start putting other things in the seed mix then you have most of the same problems as with pellets. And too many seeds is bad for your bird the same as too many pellets are bad for it.
Since your bird is already accustomed to pellets, then make the gloop and mix some pellets in it when you serve it until the bird begins to eat the gloop and then stop giving the bird pellets. Don't get rid of the pellets until the bird is eating the gloop and then a seed mix for dinner.
As for getting a bird to eat a foods that it has never eaten before it helps if you are willing to sit down and eat some of the same food that you are offering to them to eat. This is because that is how the parent bird teaches the young bird what to eat and how to eat it. Eating for a parrot is also a social and a bonding activity. It will be needed in order to get the bird to start eating all of the fresh produce that it needs to learn to eat.
viewtopic.php?f=8&t=12521 Here is a link that will help you as it contains a listing of poisonous and non poisonous foods, trees, woods, plants and household items. The list begins on the second page of the topic.