Preheat oven to 375º. In a large pot of salted boiling water, cook
pasta according to package directions until al dente, less 2
minutes. Drain and drizzle a bit of olive oil to prevent noodles
from sticking together.
In a large pot over medium-high heat, heat oil. Cook ground beef
until no longer pink, breaking up with a wooden spoon. Remove from
heat and drain fat. Return beef to skillet and add garlic and
oregano and cook, stirring, for 1 minute. Season with salt and
pepper, then add marinara and stir until warmed through.
Combine ricotta, 1/4 cup Parmesan, parsley, and egg in a large
mixing bowl and season with salt and pepper. Set aside.
In a large casserole dish, evenly spread a quarter of the meat sauce
across the bottom of the dish, then top with a single layer of
lasagna noodles, a layer of ricotta mixture, and a single layer of
mozzarella. Repeat layers, topping the last layer of noodles with
meat sauce, Parmesan, and mozzarella.
Cover with foil and bake for 15 minutes, then increase temperature
to 400º and bake uncovered for 18 to 20 minutes.