Ok, here’s a basic technique that makes prep work a lot easier for basically any type of cooking. I’ve found that this isn’t a really common piece of knowledge and it really makes chopping onion a lot easier.
Then you want to cut the tip end off and start peeling back layers until you end up with a nice creamy white color (the green areas have a tendency to be a little tough, it’s worth losing an entire layer to get rid of a little green). If you’re prone to cutting yourself, leave the root end on the onion and use the peeled back layers as a handle of sorts. If you want to live on the edge, you can cut the root end off too.
The standard method for this is to cut vertical then horizontal slices through the onion. I find that more often than not, this makes the onion fall apart more than necessary, so I use a modified version of that. I make slices towards the center using a radius, kind of like pie slices. See photo. Anyway, you want to cut these almost all the way through the onion, but use the root end to hold them together.
Once you have those slices (the root end of the onion should hold them all together), start slicing the onion perpendicular to your other slices. This gives you the size of chunks you want. If you want smaller pieces, adjust the size of the chop, either initially, or on this step. This step of chopping is easier to make smaller than the first. I hope that made sense.