Bring a large pot of water to a boil. Add the noodles and cook them until they are a little less than "al dente". When cooked, drain and cool.
While the noodles are cooking, brown the meat and onion over medium heat in a skillet. When cooked, drain the excess grease and cool.
In a medium bowl, combine the cottage cheese, egg, 1 Tbsp Italian seasoning, and 1 1/2 cups mozzarella cheese.
Combine the spaghetti sauce with the cooled meat and set aside 1/3 of the sauce mixture. *If the casserole will be sitting in the fridge for a couple days, add a little extra sauce so it doesn't dry out.
Combine the rest of the sauce mixture with the cheese mixture and the noodles.
Grease a 9x13 pan and pour the noodle mixture into the pan. Spread the rest of the sauce over the noodles then sprinkle the rest of the mozzarella cheese on top. *Try to cover all of the noodles with sauce and cheese so they won't dry out.
Cover and bake immediately or refrigerate or freeze until ready to use.
If baking immediately, bake at 375°, covered for 15 minutes then uncovered for another 10-15 minutes.