Heat 1/2 the oil a large frying pan over medium heat. Add mushrooms and onions; cook and stir for about 4 minutes, just until mushrooms begin to give up their juices. Stir in bread cubes and oyster sauce; cook and stir 1 minute. Remove mixture from pan and set mixture aside to cool. Wipe pan clean.
Beat egg and mix into mushroom mixture. Season to taste with salt and pepper.
Add remaining oil to frying pan and place over medium heat. Spoon mixture into frying pan in 6 equal amounts. Brown one side, flip over and brown other side. Serve.