Preheat oven to 400°f.

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Heat oil in a large saucepan over medium heat.  Add onion and allow it to cook for about 5 until soft but not browned.  Add the garlic and mushrooms, then cook a minute longer before adding spinach.  Cover pan and allow the spinach to wilt, stirring occasionally.

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Once the spinach is wilted, remove the lid and cook until most of the liquid in the pan evaporates.  Remove from heat and set aside to cool.

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Once cool enough to handle, combine spinach mixture with sausage, 1 1/4 cups mozzarella cheese, and cottage cheese.  Season to taste with salt and pepper.

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Stuff the manicotti shells with a spoon, or using a pastry bag.

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Cover the bottom a 9″ by 13″ casserole dish with 1/2 of the marinara sauce.  Arrange the manicotti in the pan then cover with remaining marinara sauce.

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Cover tightly with aluminum foil and bake for 30 minutes.  Remove the foil and sprink reminaing mozzarella cheese over the top of the of the pasta.  Return to oven for anoth 10 to 15 minutes, or until cheese is bubbly and slightly golden.

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Serve hot!