Heat oven to 350°F. In 8-inch skillet, cook beef and onion over medium-high heat until beef is thoroughly cooked, stirring frequently; drain. Stir in 1/2 cup of the pasta sauce. Remove from heat.
In bottom of ungreased 8-inch square (2-quart) glass baking dish, spread 3 tablespoons of the remaining pasta sauce. In medium bowl, beat egg white. Stir in ricotta cheese, Parmesan cheese, oregano and 1/2 cup of the mozzarella cheese.
Spread 1/4 each of ricotta mixture, spinach leaves and beef mixture over each lasagna noodle. Starting with short side, gently and loosely roll each noodle; place seam side down over sauce in baking dish. Top roll-ups with remaining sauce. Cover with foil.
Bake 30 to 40 minutes or until bubbly and thoroughly heated. Remove foil; sprinkle with remaining 1/4 cup mozzarella cheese. Bake an additional 2 to 4 minutes or until cheese is melted. Let stand 5 minutes before serving.