Place the onion slices in a bowl with vinegar and set aside.
In a pan over medium heat, fill with just enough frying oil to cover the bottom of the pan.
Place sliced salami on the pan and fry on both sides until crispy.
Place sliced cheese on the pan and fry on both sides until crispy.
Crack the egg over the pan and fry on both sides until cooked.
Carefully add the onion slices and half of the vinegar to the pan and cook until the onions are translucent.
Slice the bagel and optionally toast, then assemble with a layer of mayoketchup, fried egg, fried cheese, fried salami, fried onions, avocado slices, and another layer of mayoketchup.