Combine the shredded chicken, chopped spinach, cottage cheese, 1 cup of mozzarella, 1 teaspoon of Italian seasoning, salt, and pepper, and set aside.
Cook the pasta so it is a little undercooked. Once they are cooked rinse them with cold water and cool them.
While the pasta is cooking make the red sauce. In a skillet heat the olive oil. Add the onion, green pepper, and garlic. Cooking over medium heat cook the vegetable until they begin to soften.
Add the diced tomatoes, tomato sauce, 1 1/2 teaspoons Italian seasoning, and Parmesan cheese and stir until well blended. Bring to a boil then turn down the heat and simmer while preparing the shells.
Preheat oven to 350 degrees F.
To assemble - spread enough of the red sauce on the bottom of a 9 x 13-inch pan to cover it well. Fill the cooked shells with about a heaping tablespoon of the chicken filling. Place the stuffed shell in the baking pan on top of the red sauce. Repeat the procedure for the rest of the shells.
Drizzle the remaining red sauce over top of the stuffed shells. Sprinkle the remaining mozzarella on top.
Bake in the preheated oven for 30 to 35 minutes until the cheese is melted and lightly browned.