In a large skillet over medium heat cook the ground beef, onion, and garlic until brown. Add the spaghetti sauce, tomato sauce, tomato paste, salt, and Italian seasoning and stir until well incorporated. Cook until heated through.
In a large bowl mix together the ricotta cheese, egg, grated Parmesan cheese, and 1 cup shredded mozzarella cheese.
Spray the crock with nonstick spray. Spoon a layer of the meat mixture onto the bottom of the slow cooker. Add a layer of the uncooked lasagna noodles. Break to fit noodles into slow cooker. Top noodles with a portion of the cheese mixture. Next layer 2 cups spinach and 1/3 of the zucchini. Repeat the layering of sauce, noodles, cheese and veggies until all the ingredients are used. Top with remaining 1 cup of mozzarella. Drizzle water around the edges of the crock.
Cover, and cook on LOW setting for 5 to 6 hours.
Let sit for 30 minutes or more and then slice and serve.