Cook noodles according to package directions, without adding the salt and fat. Drain.
Heat a large Dutch oven over medium heat. Add oil to pan-swirl to coat. Add onion and carrot. Cook 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.
Remove pan from heat. Stir in noodles, peas, just over half of your 2/3 cup parmesan, and tuna. Spoon mixture into a 9x13 casserole dish coated with cooking spray.
Sprinkle shredded cheese over mixture. (If seriously cutting down on fat, this ingredient and step can be omitted.)
In a small bowl, combine the bread crumbs and remaining parmesan. Sprinkle crumb mixture evenly over the casserole.
Bake in preheated 400 degree oven until bubbly and cheese is melted. About 10-15 minutes.