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Preheat oven to 400°F Meanwhile, bring a large pot of salted water to a boil, add noodles and cook until al dente, 8 to 10 minutes.
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Drain well and gently transfer to a clean work surface.
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Grease a small roasting pan or casserole dish with cooking spray; set aside. Working with one noodle at a time, spread with about 2 tablespoons of the ricotta and 2 tablespoons of the marinara then top with spinach.
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Starting at one end, roll up noodle snugly then arrange in pan either seam-side down or with the rolls close enough together to hold each other closed.
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Pour remaining marinara over assembled rolls then sprinkle with mozzarella and bake until golden and bubbly, 20 to 25 minutes.