Fry the bacon on a cast iron pan on medium heat until crisped, about 7 minutes, then remove from the heat and place on paper towel to drain. Leave the bacon fat in the pan.
Chop 3 slices of bacon into small pieces and place them in a large bowl with the egg, beef, spices, oil, and bread crumbs.
Gently mix with your hands until combined.
Turn up the heat on the pan to medium high, and form the burger mixture into four equal patties.
Place the patties on the cast iron and add the sliced mushrooms to the grill beside the patties.
Cook the burgers for 4 minutes, then flip once they've formed a crust.
Press the burgers down with a spatula and cook for 2 more minutes.
Add a slice of cheese to each burger, and continue to cook for 2 more minutes.
Top with the mushrooms, remaining reserved bacon, and serve on buns with condiments of your choice.
