Brown the beef. Cook in a skillet over medium heat for 8 to 10 minutes, then drain. Add vegetables. Cook the onions, garlic, carrot, and celery for 5 minutes, until soft.
Simmer. Stir in the mushrooms, sauce, water, salt, pepper, and oregano. Simmer for 10 minutes.
Mix the cheese. Stir the ricotta, egg, grated Parmesan, and parsley together.
Layer. In two 9x13 inch dishes, layer sauce, 3 noodles, cheese filling, and mozzarella three times. Finish with sauce, mozzarella, and Parmesan.
Freeze (optional). Wrap each pan in plastic wrap and foil.
Bake. Thaw if frozen. Bake covered at 375 degrees F for 45 minutes, then uncovered for 15 minutes, until 165 degrees F in the center.