The American falafel sandwich is a food-cart sandwich whose hardest engineering problem is the gap between the fryer and the customer's hand. Fried chickpea fritters in a pita with tahini, chopped salad, and hot sauce is the build, and the fritter is the only crisp thing in it: the moment it goes into a warm pocket against wet sauce and cut tomato, it starts to soften, so the whole assembly is arranged to keep that window as short and the shell as defended as possible. On a busy cart line, the sandwich is built to be handed over while the crust still has snap.
The craft is in the fritter and the order of assembly. The falafel is ground from soaked chickpeas with herbs and aromatics and fried hot so the outside sets into a craggy shell while the inside stays green and steamy; fried too cool it absorbs oil and goes heavy, fried right it stays light enough to stack several into one pocket. The pita is the carrier and the limiter: a pocket pita has to be sturdy enough to hold a loose, wet load without blowing out the seam, and it is often warmed so it folds rather than cracks. Tahini is thinned to a sauce that coats without drowning, the salad of tomato, cucumber, onion, and parsley supplies the cold acid and crunch the fritter lacks, and the hot sauce is the cart's signature, applied last and to the eater's tolerance. The fritters are crushed slightly as the pocket is filled so they knit with the sauce instead of rolling out the open end.
The variations are the cart's own dialect. A version swaps the pita for a wrap in a flat lavash or pressed flatbread for a tighter cylinder; another adds pickled turnips or amba for a sharper edge; a platter build drops the bread entirely. Each is its own build and deserves its own article rather than being crowded in here.