Heat oil in a sauté pan over medium heat. Add onions and sauté until nicely browned and caramelized. This can take about 15-20 minutes. Once caramelized, add the thinly sliced pastrami and facon. Mix and sauté another 2-3 minutes. Add brown sugar. Mix and remove from heat. At this point you can also refrigerate or freeze the mixture for later use.
Preheat oven to 350℉. For easier serving, score down the crusts almost through so they will slice easily once done. Another tip for easier serving is to prepare a rectangle made out of heavy duty silver foil for easier transferring (see images).
Place crusts on prepared foil on a baking sheet and smear garlic dip generously over the surface. Top with pastrami mixture. I like to strain the meat mixture in a strainer to remove as much fat as possible, but you don't have to do that, you can simply use a slotted spoon to lift the meat from the pan, leaving the fat behind (the fat in the pan comes from the facon). Drizzle with BBQ sauce. Bake for 20 minutes.
I like to use the plastic containers that come with the pizza bread to store the pizza in the refrigerator until ready to serve.
To serve: Either serve immediately, or, if serving on Shabbos, refrigerate and then bring to room temperature or place over the cholent or hot plate. The meat pizza freezes well, and reheats well. You can also prepare the pastrami mixture in advance and assemble/bake it fresh.