Heat a generous amount of oil in a sauté pan over high heat. Add onion and sauté until golden at the edges, stirring occasionally.
Drain excess oil. Add pastrami and BBQ sauce and toss to combine. Make sure to separate the pieces of pastrami so they cook individually. Sauté for 2-3 minutes. Transfer to an aluminum loaf pan.
Place the pan on the grill and let it sit for 10-20 minutes while you grill the rest of your food. Top your favorite burgers with pastrami topping.