All chickens are different and will prefer different treats. I think any produce is great- whatever they prefer. Keep a good variety for some great nutritious tasty eggs. I wouldn't do anything overly spicy or smelly though- could flavor your eggs. I've also read that they won't eat citrus fruit.
There isn't much a chicken can't eat. As shown by the very short list of unsafe items in the treat chart. I'd mostly just avoid anything potentially toxic but I also wouldn't feed several things in very large amounts. Make sure it only amounts to a treat and not a significant portion of their diet. Chickens don't notice spicy things and it shouldn't bother them. People feed rather strong pepper to deworm them and increase egg laying.
Last year, I steamed and froze pumpkins, including the jack o'lanterns, for the chickens' winter treats. The pumpkin was greatly appreciated in the hen house.
My chickens like tomatoes but cherry tomatoes are a special favorite. They grab one and run . . . keep away
The sparrows moved in pretty hard on our peach tree this year. Probably one-third of the fruit had sparrow damage. Hard enuf for me to harvest the good fruit and I just left what had been damaged. When it fell to the ground, the chickens laid into it with a vengeance! After about a week, they'd cleaned up all the fallen peaches.
Lettuce was a very early treat for the chicks. They all enjoyed this green food before they could get out on their own and forage in the backyard. The lettuce and veggie garden is not in my backyard.
Out on the lawn, they eat a lot of grass. They will eat a little lettuce but nothing like in the days before foraging. Lawn grass seems to provide for most of their need for leafy greens.