Preheat the oven to 375°F (190°C).

Bring a large pot of salted water to a boil and cook the lasagna noodles according to package instructions until al dente.

In a skillet over medium heat, brown the ground beef until fully cooked. Drain excess fat.

In a mixing bowl, combine ricotta cheese, egg, oregano, salt, and pepper.

Spread a thin layer of marinara sauce on the bottom of the baking dish. Layer 4 noodles, half the ricotta mixture, half the meat, and a third of the mozzarella.

Continue layering with another layer of noodles, remaining ricotta, remaining meat, and another third of mozzarella. Top with the final layer of noodles, remaining sauce, and all the mozzarella.

Sprinkle the grated Parmesan cheese over the top.

Cover the dish with aluminum foil and bake for 25 minutes, then remove the foil and bake for an additional 20 minutes.

Let the lasagna rest for 10-15 minutes before slicing.