In a medium skillet over medium-high heat, cook the ground beef, breaking it up with the back of a spoon or spatula, until browned, about 4 minutes. Drain off any excess fat. Add the garlic and grated onion and cook, stirring, for 1 minute. Add the tomato paste, parsley, salt, cayenne, cumin, paprika, and cinnamon and cook, stirring, for 1 minute more.
Arrange the flatbreads, naan, or pita on a rimmed baking sheet and spoon the ground beef on top, spreading it almost to the edges. Bake until the edges of the flatbreads are beginning to crisp and brown, 4 to 8 minutes. (For a softer flatbread, bake for just 3 to 4 minutes. For a crisper flatbread, closer to 7 to 8 minutes.) Remove the flatbreads from the oven.
Top each flatbread with a few strips or slices of cucumber, a dollop of yogurt, a sprinkling of parsley or cilantro, and a few slices of red onion. Serve with a couple of lemon wedges on the side for squeezing over the top.
*CAN I SUBSTITUTE GROUND LAMB FOR GROUND BEEF?
You can easily substitute an equal amount of ground lamb for the beef. You can also use this spiced ground beef mixture as a filling for soft or hard-shell tacos.