Cook the bacon first and drain it on paper towels. Reserve the bacon grease for cooking. In the same pan, cook onions for about 5-7 minutes, until soft. Remove and set aside. In the pan, add some bacon grease, and crack eggs, season with salt and pepper, and cook for about 4-5 minutes.
Toast the bagels until they are lightly browned and spread a thin layer of butter on top.
On the bottom half of the bagel, add the cheese slices, onions and bacon, then top with the fried egg. Place the top half and enjoy.