In large skillet over medium heat, in hot oil, cook onion, garlic and Italian seasoning until onion is tender. Stir in spinach, cook until tender and liquid evaporates. Remove from heat and stir in soup, Italian cheeses and egg. Set filling aside.
In medium bowl, stir together spaghetti sauce and sour cream; pour ½ of the sauce mixture into 13 x 9 inch baking dish. Set remainder aside.
Arrange 3 lasagna noodles over sauce, spread with ½ of the filling. Sprinkle with 1/3 of the mozzarella. Arrange 3 more noodles over cheese; spread with remaining filling. Sprinkle with another 1/3 of the mozzarella. Top with remaining 3 noodles and remaining sauce.
Bake at 350 degrees for 40 minutes. Sprinkle with remaining 1/3 of the mozzarella; bake 5 minutes more. Let stand 15 minutes before serving.