Pour 1 1/2 cups milk into a saucepan; cook over medium heat 1 minute or until warm. Whisk remaining 1 cup milk and flour in a bowl until flour dissolves. Add to pan; cook, stirring constantly, 8 minutes or until bubbly. Reduce heat to low; add cheese, salt, black pepper, and nutmeg. Stir until cheese melts.
Add corn, roasted red bell pepper, and cheese sauce to noodles. Spoon mixture into an 11 x 7-inch baking dish coated with cooking spray.
Place bread in a food processor; pulse 5 times or until coarse crumbs measure 1/2 cup. Combine breadcrumbs and melted butter; sprinkle over noodle mixture. Bake at 450° for 10 minutes or until golden brown and bubbly.