Bring a large pot of salted water to a boil.
Cook the lasagna noodles according to package instructions.
Drain and lay them flat on a baking sheet to prevent sticking.
Heat olive oil in a large skillet over medium heat.
Add the ground beef and cook until browned, breaking it apart with a spoon (about 5–7 minutes). Drain excess fat if needed.
Add the diced onion and cook for 3 minutes until softened.
Stir in the minced garlic and cook for another minute.
Pour in the crushed tomatoes, tomato sauce, Italian seasoning, salt, and black pepper.
Simmer for 10 minutes, stirring occasionally.
In a mixing bowl, combine ricotta cheese, egg, Parmesan cheese, and dried parsley. Stir until well blended.
Preheat your oven to 375°F (190°C).
Spread a thin layer of meat sauce at the bottom of a 9x13-inch baking dish.
Lay 3 noodles over the sauce.
Spread ⅓ of the ricotta mixture over the noodles.
Sprinkle ⅓ of the mozzarella cheese on top.
Repeat the layers two more times, ending with a layer of noodles topped with meat sauce and the remaining mozzarella cheese.
Cover the dish with aluminum foil and bake for 30 minutes.
Remove the foil and bake for another 10–15 minutes until the cheese is bubbly and slightly golden.
Allow the lasagna to rest for 10 minutes before slicing.
Serve warm with your favorite sides.