Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain. Place manicotti on a sheet of waxed paper or aluminum foil to cool.
Grill red bell pepper until its skin had dark spots and is tender; place on a plate to cool. Grill mushrooms until tender and most of the moisture is gone; place on a cool plate. In a medium bowl, combine ricotta cheese, 1 1/2 cups of mozzarella cheese, egg, salt and pepper to taste, Italian seasonings and garlic powder; mix well.
Preheat oven to 350 degrees (175 degrees C).
When cool chop mushrooms and add to cheese mixture. When peppers are cool, pinch skin and pull away; dice and place in cheese mixture.
In a 9x13 inch baking dish place a thin layer of the spaghetti sauce on the bottom. Stuff manicotti with mixture and place the manicotti in the baking dish. Pour the spaghetti sauce on top of the noodles and sprinkle with 1/2 cup of mozzarella cheese. Bake in preheated oven for 20 minutes.