Heat oven to 350°F. Spray 13x9-inch (3-quart) glass baking dish with cooking spray.
In 5-quart Dutch oven, cook and drain spaghetti as directed on package; set aside. In same Dutch oven, melt butter over medium heat. Stir in flour, salt and pepper. Cook and stir over medium heat until smooth and bubbly. Gradually stir in half-and-half. Heat to boiling, stirring constantly; boil 1 minute. Remove from heat.
Add cooked spaghetti, bacon, peas and 1 cup of the cheese; toss to coat spaghetti. Stir in egg. Spoon into baking dish. Sprinkle with remaining 1/2 cup cheese.
Bake uncovered 20 minutes or until set and edges are bubbly. Sprinkle with parsley. Cut into squares to serve.