Bring a large pot of salted water to a boil. Add the manicotti shells and cook until al dente, about 8-10 minutes. Drain and toss with a little olive oil to prevent sticking. Set aside.
In a bowl, combine the low-fat ricotta cheese, 1 cup of the shredded mozzarella, the grated Parmesan, the egg whites, and the dried oregano. Stir in the cooled meat mixture until evenly combined.
Mix the Italian seasoning into the marinara sauce, then spread 1/2 cup of the mixture on the bottom of a 9×13-inch baking dish. Using a spoon or piping bag.