Good morning, it's nice to have you here!
This is a list from an article in the Learning Center on which treats to avoid (it's more than just vegetables):
Do not feed your chickens the following:
• Avocado
• Candy
• Chocolate
• Citrus [a little won’t hurt your birds but in general it’s best to avoid]
• Certain herbs [most herbs are fine and healthy to feed your birds. However avoid the following: Azalea, Philodendron, Rhododendron, Sweet Pea, Black Nightshade, Foxglove, Oleander, Castor Bean, Vetch, Henbane, Irises, lantana, St. John's Wort, Trumpets Vine, Morning Glory, Datura, Clematis and Honeysuckle.]
• Leaves from tomato or nightshade plants
• Nuts
• Onion
• Raw beans
• Raw egg
• Raw meat
• Raw potato
• Rhubarb
• Salt
• Spoiled, rotten, or moldy foods
Here's a link to the complete article if you care to read it:
https://www.backyardchickens.com/articles/table-scraps-and-leftovers-for-chickens.74549/