Brown the beef and onion for 10 minutes until the beef reaches 160°F, drain, and stir in the garlic, crushed tomatoes, tomato sauce, oregano and 1 1/2 teaspoons salt.
Mix the ricotta, egg, 1/2 cup Parmesan and remaining salt.
Spread 1 cup beef sauce in a buttered 6-quart crockpot and layer one-third each of the broken noodles, ricotta mixture, remaining sauce and mozzarella.
Repeat the layers twice, ending with mozzarella and the remaining Parmesan.
Cover and cook on low for 4 to 4 1/2 hours until the center noodles are tender, then rest uncovered for 20 minutes before cutting.