I'd start out with putting the chopped onions in a frying pan with water, just enough to cover the onions. Then let boil until the onions are clear and soft. Let the water boil off before adding the honey, then once you add the honey bring to a rapid boil again (boiling honey is what makes the honey medicinal), set aside and let it cool down to room temperature.
My favorite recipe for bronchitis is my hot toddy recipe. I don't know if you found it on my website, if not, you can find it if you go to the button on the left that reads "Home Remedies" then go to the link that says "Chest Congestion & Nagging Cough". I use my hot toddy's on everybody in the family. It not only relieves the cough but it also helps you get that much needed rest.