Cook the manicotti noodles per the directions on the box. Gently rinse in cool water to stop the cooking and to get the shells cool enough to stuff. Set aside.
In a skillet over medium heat, warm the oil and then saute the mushrooms until soft.
In a medium bowl combine ricotta cheese, parmesan cheese, beaten egg, parsley, cooked mushrooms and 1/2c mozzarella shreds. Stir well to combine.
Gently stuff the cool shells with the mixture. Place stuffed shells into an oiled 9X13 casserole dish. Once all stuffed shells are in the baking dish. Top with the pasta sauce.
Bake covered at 375 Degrees F for 40-45 minutes. Then uncover, add the remaining 1/2 cup of cheese to top and bake for 5 more minutes.
Let stand for 10 minutes. Top with more parsley and serve!