While slow cookers are often thought of as 1970s throwbacks and only good for making heavy stews, Jessica Seinfeld uses hers to make everything from whole small chickens to oatmeal and even this worry-free lasagna.
In a medium bowl, combine the tomatoes, garlic, oregano, salt, red pepper and black pepper. In a separate bowl, mix the ricotta, 1 cup of the mozzarella and Parmesan.
In the bottom of a 5- to 6-quart slow cooker, spread a thin layer of the sauce. Top with 3 of the noodles (breaking to fit as necessary). Spread about 1 cup of the sauce over the noodles and layer with 2 cups of the spinach and 1 1/2 cups of the cheese mixture. Repeat twice more with the noodles, sauce, spinach and cheese mixture. Top with the remaining 3 noodles, sauce and 1 cup mozzarella.
Cook on low, covered, until the noodles are tender—especially in the center of the lasagna—about 3 to 3 1/2 hours.
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