Preheat oven to 375°F (190°C).

Make the Sauce: In a large skillet over medium-high heat, cook ground beef and chopped onion until beef is browned. Drain excess grease. Stir in minced garlic and cook for 1 minute. Add crushed tomatoes, Italian seasoning, salt, and pepper. Simmer for at least 15 minutes.

Prepare Cheese Filling: In a medium bowl, mix together ricotta cheese, 1/2 cup of the Parmesan cheese, the egg, and fresh parsley. Season with a pinch of salt and pepper.

Cook Noodles: Cook lasagna noodles according to package directions until al dente. (Skip if using no-boil noodles).

Assemble: Spread 1 cup of meat sauce in the bottom of a 9x13 inch baking dish. Layer with noodles, half of the ricotta mixture, 1/3 of the mozzarella, and 1/3 of the meat sauce. Repeat the layer. Top with a final layer of noodles, the remaining meat sauce, the remaining mozzarella, and the remaining 1/2 cup of Parmesan cheese.

Bake: Cover with foil and bake for 25 minutes. Remove foil and bake for an additional 20-25 minutes, until the top is bubbly and golden brown.

Rest: Let the lasagna rest for 10-15 minutes before slicing and serving.