Lavash is available in the kosher section of supermarkets. You can also use Afghan bread, sometimes called Kabul bread, but it's a little thick. You also could try the Indian bread naan.
First, sprinkle a thin scattering of shredded, regular mozzarella on the flatbread. Next, place 20 little slices of fresh mozzarella evenly across the rectangular flatbread, with the idea of eventually cutting the pizza into three-by-three inch squares that each contain a piece of the cheese.
Top each cheese with a ring or a couple strips of the caramelized onions. Place a bite-size piece of tasso atop each onion pile, and a few bits of diced scallion into the cheese next to each piece of ham. All ingredients should touch the cheese, so as to be adhered to the flatbread.
Bake at 400 for about 7 minutes, until breads and toppings are quite browned and crispy. Remove to a rack; cool. Cut pizzas with a chef's knife, using a rolling motion.
You can use a wide variety of toppings. There are three secrets: One, you must devise a way to glue your ingredients to the flatbreads; this is easily done with mozzarella cheese. Two: avoid putting on too much of anything, especially cheese; get too thick, and the bread won't support the toppings and could lose its crispiness. The third secret: avoid using ingredients that are going to leak a bunch of water or oil during cooking; this can soak into your crusts and make them soggy (or, in the case of most pepperoni, can create an unattractive slick of orange-dyed grease).
Almost anything goes. Think about using just three or four cheeses, veggies, and meats in ways that create contrasts in color, flavor and texture. For instance: chunks of tasso ham (salty, spicy), caramelized red onions (sweet), fresh mozzarella (gooey), scallions (crispy and fresh).
Other possible combos include: 1. Cherry-tomato halves, fresh basil slivers, chunks of fresh garlic, mozzarella, bell pepper strips (red, orange, yellow and green) with chunks of cooked Italian sausage, mozzarella and fresh parmigiana, 2. Bell pepper strips with whole kalamata olives and mozzarella.