In a blender, combine the tomato sauce with the chicken broth, brown sugar, Worcestershire sauce, mustard, chipotle and adobo sauce and puree until smooth. Pour the sauce into a large skillet. Stir in the crumbled meat loaf and bring to a simmer over moderate heat. Season with salt and pepper. Spoon the meat onto the buns, top with sliced onion and pickles, close and serve.