Corned Beef & Cabbage Turnovers

canola oil

medium sweet onion, finely chopped (about 1 cup)

coleslaw mix (12 ounces of shredded cabbage & carrot)

cooked corned beef, chopped finely

salt and pepper,

sheets (one 17.3-ounce package) frozen puff pastry, thawed

large egg

mayonnaise

Dijon mustard