Instructions

 Preheat oven to 350 degrees. Spray a 9x13 casserole dish.

On the stove use a large pan/skillet to melt butter; add onion and garlic. Cook until onions become translucent.

Add flour, stir rapidly while doing this.

Then add milk, diced tomatoes and tomato sauce.

Simmer on low for 7 to 8 minutes.

Stir in chicken, ½ of the mozzarella, salt and pepper.

Mix everything well and the transfer into 9x13 pan.

Cover with remaining cheese.

Bake (uncovered) for 20 to 30 minutes.