Preheat a grill or a large rectangular grill pan over medium heat. Brush the grill grates or grill pan will canola oil before the grilling bread
Roll out the dough with a rolling pin on a floured work surface into a long rectangle, about 1/4-inch thick. Put the dough onto the grill or gill pan and grill for 3 minutes per side. Remove the bread from the grill and put on a sheet pan.
Preheat the oven to 475 degrees F
Brush the grilled flat bread with the Chicken Souvlaki marinade. Top with onion, tomato, chicken, and feta cheese. Bake until flat bread is cooked through and the cheese is melted, about 10 minutes
Remove from oven and let cool for 2 minutes. Drizzle with Tzatziki Sauce, slice and serve.