Preheat the oven to 375°F. Boil the lasagna noodles in a large pot of salted water until al dente, then drain and set aside.

In a large skillet over medium heat, cook the ground beef until browned, breaking it up as it cooks. Drain excess fat, then stir in the marinara sauce, oregano, salt, and pepper. Simmer for 5 minutes.

In a mixing bowl, combine the ricotta cheese, egg, and half of the Parmesan cheese. Stir until smooth.

Spread a thin layer of meat sauce in the bottom of an 8x8 inch baking dish. Place 2 noodles on top, followed by half the ricotta mixture, a layer of meat sauce, and a handful of mozzarella.

Repeat the layering with the remaining noodles, ricotta mixture, meat sauce, and mozzarella. Finish with the last noodles, remaining meat sauce, mozzarella, and the rest of the Parmesan.

Cover the dish with foil and bake for 25 minutes. Remove the foil and bake for another 10 minutes until the cheese is bubbly and lightly browned.

Let the lasagna rest for 10 minutes before slicing and serving.