Place the chicken breast, onions, mushrooms, broth, and seasonings in a crockpot and cook on high for 4 hours or low for 8 hours. At the end of that time, drop the block of cream cheese into the crockpot and put the lid back on. Allow the cream cheese to melt while you cook the noodles in hot water on the stove. When the noodles are almost done, stir the cream cheese in with the other ingredients in the crockpot until smooth (which shreds the chicken in the process), then drain the noodles and add them in along with the mozzarella. Give it all a good stir and serve while hot. Top with more shredded mozzarella if desired.