Precooked onions depend on what you’re trying to achieve with them. Caramelized is another story too.
I have noticed that simply coating the balls of dough with a bit of oil before proofing changes the color of the finished dough; a little more char.
Biggest thing, unfortunately, is high heat. Before I got a pizza oven, I was experimenting with two stones. One on top of the pizza. They need to be really hot, not just in the oven for a while.