1. Preheat broiler.
2. Cook noodles according to package directions, omitting salt and fat. Drain. Heat a large skillet over medium heat. Add oil to pan; swirl to coat. Add onion and carrot; cook 6 minutes or until carrot is almost tender, stirring occasionally. Sprinkle with flour; cook 1 minute, stirring constantly. Gradually stir in milk; cook 5 minutes, stirring constantly with a whisk until slightly thick. Stir in cream cheese, mustard, salt, and pepper; cook 2 minutes, stirring constantly.
3. Remove pan from heat. Stir in noodles, peas, 1/4 cup Parmigiano-Reggiano cheese, and tuna. Spoon mixture into a shallow broiler-safe 2-quart baking dish coated with cooking spray; top with remaining 1/4 cup Parmigiano-Reggiano cheese. Broil 3 minutes or until golden and bubbly. Let stand 5 minutes before serving.