I don't know what onion leaves are. But if you google "whether

to you cats", you'll see the consensus is to avoid them.  I think occasional garlic may be fine, but I would not risk onion or avocado.  Even if they don't make your cat sick right away, they are potentially dangerous in the long run.  Plus, cats don't need these things.  If you want to feed your cat some vegies, napa and kale are much better choices.