Preheat oven to 375 degrees. Score the duck skin with a knife, then place duck legs in a small roasting pan or casserole dish. Sprinkle evenly with salt and pepper. Add orange juice, maple syrup and 2 tablespoons of the ancho chili powder, turning the duck legs a few times to evenly coat, ending with the skin side up. Press equal amounts of orange zest onto exposed portion of each leg. Roast for 90 minutes, turning twice.
While the duck roasts, make the other accompaniments. Thinly slice the tomatoes and set aside. Toss the Romaine lettuce with the cilantro and set aside. Bake the flatbread on a large baking sheet for 7-10 minutes or until crispy and light golden brown. (This can be done while the duck cooks, simply use the second rack in your oven.)
When the duck has finished cooking, remove the legs from the pan and shake off excess liquid and set on a cutting board to cool. Pour 2/3 cup of the cooking liquid into a small saucepan, add the remaining 1 tablespoon of ancho chili powder and bring to a boil. Reduce by half, remove from heat and stir in the sour cream.
When the duck is cool enough to handle, shred the meat and skin into bite-sized pieces.
To assemble, add equal amounts of tomatoes, Romaine, duck and Manchego to half of the flatbread slices, drizzle with reduced cooking liquid, then top with remaining flatbread slices. Serve immediately.