1. Preheat oven to 350 degrees Fahrenheit.
2. Place pie shells on a baking sheet and bake for seven minutes.
3. While the pie shells bake, heat oil in a sauté pan over medium heat. Add onion and sauté until soft, five to seven minutes.
4. Add coleslaw mix and sauté until wilted. Stir in pastrami.
5. Remove from heat and mix in mayonnaise, flour, eggs, salt, pepper, and mustard.
6. Add filling to pie shells and return to the oven for an additional 20 minutes, or until filling is set.