cook butter, onion, and garlic over medium heat until translucent. Add flour stir and cook until golden in color, add milk and evaporated milk. Bring to a simmer, add nutmeg, sugar, Parmesan cheese, salt, and pepper. simmer about 10 min.
Meanwhile bring water to a boil add salt and pasta cook about 10 min. Drain.
At the same time cut up chicken and toss with oil. Heat a griddle or skillet over medium high heat until when water is dropped on skillet and it boils away without dancing to much, about 450 degrees. add chicken stiring constantly until cooked, this usually takes about 4-7 min. depending on exact temps and size of meat.
If you timed it right everything up to this point will be done at the exact same time. Put sauce, pasta, chicken, and 1/2 cup of mozzerella into an extra-large mixing bowl. Stir to combine. Put into a 9"x13" cake pan, top with remaining mozzerella, parmesan, and herbs. Bake in a 400 degree oven until cheese is slightly golden brown. allow to rest 5-15 min. Serve.