1 tablespoon olive oil
1 small onion, chopped
6 cloves garlic, minced
8 ounces crimini mushrooms, chopped
28 ounce can crushed tomatoes*
14.5 ounce can petite diced tomatoes
8 ounces tomato sauce
2 teaspoons dried oregano
2 teaspoons dried basil
2 teaspoons Italian seasoning
½ teaspoon salt
⅛ teaspoon black pepper
10 whole wheat lasagna noodles (uncooked, not no-boil)
1⅓ cups part-skim ricotta cheese
5 ounces fresh baby spinach
2 ¾ cups grated part-skim mozzarella cheese
Heat olive oil in a medium skillet over medium heat. Add onion, garlic, and mushrooms and cook until slightly softened, about 3 minutes. Stir in crushed tomatoes, diced tomatoes, tomato sauce, oregano, basil, Italian seasoning, salt, and pepper. Remove from heat.
Spread a thin layer of the sauce/mushroom mixture over the bottom of the slow cooker. Place a layer of noodles over the sauce, breaking them into smaller pieces as needed. Spoon ⅓ cup ricotta cheese over the noodles, scooping little dollops of it to spread it out over the noodles. Pour 1 cup of the sauce evenly over the noodles and ricotta. Top with ⅓ of the spinach and ¾ cup mozzarella.
Repeat layers two more times: noodles, ⅓ cup ricotta, 1 cup sauce, spinach, ¾ cup mozzarella.
Then make one more layer on top with noodles, the remaining sauce, ⅓ cup ricotta, and ½ cup mozzarella.
Cook lasagna in your slow cooker on low heat for about 3 ½ hours, until noodles are tender. Let stand, covered, for 30 minutes before serving.