The easiest way to get a bird to start eating fresh food is to transition to sprouts first, and then add tiny chopped pieces of fresh produce after they'd are eating the sprouts really well. Remember that in the wild birds will test food out for several days before really making a meal of it. If during that time they feel ill, they will never eat that food again. Also, congrats in getting such a rare bird that prefers veggies to fruit! Amazons are prone to fatty liver disease so keeping the sugar down, even fruit sugar, is important. Also, you are hard pressed to fund a fruit whose nutrients cannot be found in veggies anyway, so don't sweat the fruit thing, veggies are far better for him anyway.
The only concern with the frozen veggies is making sure there are no hot spots when you warm them
I often feed them still frozen as toys, I like to feed "food toys" whenever possible. Of course there are many ways of trying to get birds to eat fresh food, but the above is what I have done with every single one of the birds I own, and the 18 foster budgies i recently rescued. It works like a charm. I have never had a bird refuse sprouts when they were done right, and birds on sprouts are much more likely to try other fresh foods. The other things about chopping it up small is that while the birds are digging for the foods they like, they are tasting the other foods and getting used to them.
Oh, also, be careful with feeding me with the pellets. Depending on certain factors, they can cause the pellets to spoil really fast. My pellets sour in under two hours when even the tiniest bit of moisture is added, but that is in Hawaii, it is probably longer other places. Just be really careful because, aside from obvious concerns, sour pellets means sour tummies, and sour tummies mean a bird who is never going to eat those veggies again.
I'm still trying different veggies and fruit as none of them are big fans...actually neither am I:54:. I've eaten more fruits and veggies since I've had my fids though
