Spray 5- to 6-quart oval slow cooker with cooking spray. Remove pie crusts from pouches; cut pie crusts in half. Press 3 pie crust halves in bottom and 2 inches up side of slow cooker, overlapping seams by 1/4 inch. Refrigerate remaining pie crust half for another use.
Cover; cook on High heat setting 1 hour 30 minutes.
Sprinkle 1 cup of the cheese, the ham and 1/4 cup onions over crust. In medium bowl, beat eggs, whipping cream, salt, pepper and nutmeg with whisk. Pour over ingredients in crust. Sprinkle with remaining 1 cup cheese.
Cover; cook on High heat setting 1 hour 30 minutes or until filling is set. Uncover; let stand 5 minutes before serving. Cut quiche into wedges; serve immediately. Garnish with tomatoes and additional onions.