Heat a large cast iron skillet or griddle over medium-high heat. Toast the bun in a few Tbsp oil or butter, remove from the pan and set aside.
Add the onion and stir, cooking until the onion is slightly translucent, 5-7 minutes.
If needed, add 1-2 Tbsp oil and burger patties, leaving alone for the first few minutes.
Flip the burgers and, using two spatulas, roughly chop the burger meat. When beef is mostly browned, add cheese and do not disturb for a few moments as the cheese starts to melt.
Chop the patties further and stir in the melted cheese. Push the meat to one side of the pan and in the open space fry two eggs to your liking.
When all elements are ready, make your sandwich by placing sliced avocado on the bun, then pile on hash browns, bacon and ground beef. Top with fried eggs. Wrap in parchment paper and enjoy!