Q.What is eating the leaves of my avocado tree
What is doing this to my avocado tree and how to treat

Certified GKH Gardening Expert
Although it looks a bit like insect damage, it also looks fungal. I would look to see if you can find any signs of, exactly, which pest it is. If you can't find any other signs than the holes, then it is most likely fungal.
Here are a few articles that will help you:
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
https://www.gardeningknowhow.com/edible/fruits/avocado/avocado-tree-growing.htm