Prep Time: 20
Cook Time: 30
Serves: Serves: 8
Cook pasta according to package directions. Drain; return to pot.
Melt butter in medium saucepan over medium heat. Stir in flour; cook 2 minutes, stirring constantly. Gradually stir in milk; bring to a simmer, stirring frequently. Stir in mustard, salt, pepper and nutmeg; simmer 1 minute more or until sauce has thickened.
Pour white sauce and, if desired, peas over pasta; toss well. Add tuna, Mozzarella cheese and 1/2 cup Cheddar cheese; toss well.
Spoon mixture into 8x8-inch pan or 2-quart casserole coated with cooking spray. Sprinkle with remaining Cheddar cheese and paprika. Bake in preheated 350°F oven 30 minutes or until hot and bubbly.