Preheat oven to 425°F.
Trim fat from chicken. Cut 1/2 lengthwise.
Place chicken pieces on a baking sheet. Season generously with paprika, seasoned salt and black pepper.
Place in preheated oven. Bake for 20 minutes.
Remove from oven and check that internal temperature is at least 165°F. Set aside to cool.
Turn oven down to 350°F.
Prepare pasta according to package directions, less 1 - 2 minutes. Drain. Set aside.
Add 3 tablespoons butter to a medium pot. Place over medium heat and melt butter.
Whisk in flour and mustard powder. Whisk well until smooth.
Once it is lump-free, stir in milk, onion, egg and 1 teaspoon paprika. Stir continuously with a whisk for about 5 minutes.
Add both cheddar cheeses to milk/onion mixture. Whisk to melt cheese and mix well.
Taste. Add seasoned salt and pepper, to taste, if needed.
Fold cooked pasta into mixture. Mix well.
Shred cooked chicken. Add to pasta. Mix well.
Pour pasta mixture into a large casserole dish. Set aside.
Melt 2 tablespoons butter in a microwave safe bowl.
Add Parmesan and bread crumbs. Mix well.
Sprinkle over prepared pasta.
Place in hot oven and bake for 30 minutes.
Remove and let cool for a few minutes before serving.
Serve hot.