Heat oven to 350°F. Spray medium nonstick skillet with nonstick cooking spray. Add ground beef, onion and bell pepper. Cook and stir until browned; drain. Reduce heat to low; stir in mushrooms and spaghetti sauce. Simmer 5 minutes, stirring occasionally.
In small bowl, combine ricotta cheese, Parmesan cheese, parsley and egg; mix well. If lasagna noodles are in perforated sheet, separate at perforations. Cut 1 of the lasagna noodles in half lengthwise.
Spread 1/4 cup meat mixture in bottom of ungreased 9x5-inch (2-quart) loaf baking dish. Top with 1 1/2 lasagna noodles, 1/2 the ricotta mixture, 1/2 the remaining meat mixture and 1/2 the mozzarella cheese. Repeat layers, starting with noodles and ending with mozzarella cheese.
Bake at 350°F. for 30 to 35 minutes or until thoroughly heated and bubbly.