Cook pasta shells in salted boiling water until al dente (use the cooking time on box.)
In a large pan or skillet, brown ground beef in olive oil; drain, return to pan, and add onion—cook until the onions just begin to soften.
Stir in Italian seasoning, pasta sauce, salt, and pepper; simmer over low heat for ten minutes.
In a large mixing bowl, add pasta and meat sauce; stir until fully mixed.
In a separate bowl, add ricotta, egg, and mozzarella; stir.
In a prepared casserole dish, alternate layers of meat sauce and ricotta mix; top with parmesan.
Bake at 350 degrees for 30 minutes or until cheese begins to brown and bubble.