Coat 9-inch pie pan with cooking spray or oil. Mix all ingredients together except Mozzarella. Press evenly into pan and up sides. Bake shell in preheated 375° F oven 10-12 minutes. If the edges start to brown, cover with foil.
Pull shell from oven. While it's hot, sprinkle and spread mozzarella cheese evenly on crust. Place back in oven just until cheese melts (about 2 minutes). The crust has a tendency to stick to the pan, so run a small knife around the edges of the crust to loosen.
Sprinkle onions over shell. Add chicken. Mix half & half, eggs, salt & pepper, mustard and nutmeg together and blend well. Pour mixture into pie crust. Top with Swiss cheese.
Bake in a preheated 375° F oven 25-30 minutes until toothpick inserted into middle of pie comes out clean.
About 5 minutes before pie is done, place the tomato slices evenly on the pie. Continue baking.