In a circular cake pan, add half of the ground beef and season with half of the garlic powder, half of the onion powder, half of the pepper, and half of the salt. Mix to combine then press the beef into patty form.
Bake for 12 minutes.
Repeat this process for the second patty.
Slice off the top of the sourdough loaf and scoop out the inside.
Begin by laying down slices of cheese at the bottom, then add your first burger patty.
Layer more cheese on top of the patty and continue by adding bacon, sauteed mushrooms & onions, spinach, and tomato.
Add a second burger patty and repeat step 7.
Place the top of the loaf back on the bread and wrap in aluminum foil.
On a level surface, use a heavy object to press the sandwich down for at least 30 minutes.