I really like onion flavored bagels.
I have not been able to re-create the same onion-y flavor as you would expect from Panera's bakery. I have come pretty close and I will share my tip.
I have tried using dehydrated onion flakes. I have also tried fresh onion minced in tiny pieces. Both with unsatisfactory results.
The most success I have had is by grating the onion with a cheese grater, dipping the bagels (after they are boiled and before they're baked) into the onion juices and spooning some pureed onion bits on top.
This method produces a satisfying onion flavor in the fresh warm bagels. The flavor fades as the bagels age, though, so there is room for improvement.
If you know of a better way to make onion flavored bagels let me know! :)