Preheat oven to 375 degrees. Grease a 9x13 inch baking pan.
In a large saucepan add beef and onion and cook until browned. Stir in garlic and cook 30 seconds. Add diced tomatoes, tomato sauce, tomato paste, pepperoni, basil, oregano, salt and pepper. Simmer on low for an hour.
In a bowl, combine ricotta, egg, spinach and parmesan cheese.
Spread 1/4 of the pasta sauce in baking pan. Add a layer of cooked lasagna noodles then spread the ricotta mixture, 1/4 of the meat sauce and top with another layer of noodles. Add 1/4 of the meat sauce, sprinkle with 1 cup mozzarella cheese and another layer of noodles.
Bake for about 45 minutes or until cheese is golden.
