Slow-Cooker Spinach & Mushroom Lasagna

Heat the oil in a large nonstick skillet over medium-high. Add the onion, and cook, stirring often, until just tender, about 5 minutes. Add the mushrooms and garlic; cook, stirring often, 2 minutes. Add the spinach; cook until the spinach just begins to wilt, about 1 minute. Remove from the heat. Sprinkle the vegetables with 1/8 teaspoon each of the salt and pepper. Add the marinara and tomato sauce, stirring to combine.

Stir together the ricotta, basil, egg, 1 1/4 cups of the Italian cheese blend, 1/4 cup of the Parmesan, and the remaining 1/8 teaspoon each salt and pepper in a bowl.

Coat the inside of a 6-quart slow cooker with cooking spray. Spread 1 cup of the marinara mixture into the bottom of the slow cooker. Arrange 3 noodles over the marinara, breaking the noodles to fit the slow cooker as necessary. Top with half of the cheese mixture and 1 cup of the marinara mixture. Repeat the layers once, beginning with the noodles and ending with the marinara mixture. Place the remaining 3 noodles over the marinara. Spread the remaining marinara mixture over the noodles. Sprinkle with the remaining 3/4 cup Italian cheese blend and 1/4 cup Parmesan. Cover and cook on LOW until the noodles are tender, 4 to 5 hours.