The tandoori chicken sandwich is built around a chicken that is deliberately dry, and the whole sandwich is the cooling answer to it. Tandoori chicken is marinated in yoghurt and red spice, then cooked fast and hot, traditionally in a tandoor, so the surface chars and stains red and the meat sets firm with very little fat or sauce left on it. The defining fact is that dryness. Most sandwich proteins bring their own moisture or grease; tandoori chicken brings heat, smoke, and a clinging spice crust and almost nothing wet, so unaccompanied between bread it reads parched and one-note. The build exists to put the moisture and the cool back, under control, without dousing the char that is the point of the meat.
The craft is restoring wetness and tempering spice with a fixed cool counter rather than diluting either. A yoghurt or mint raita is the structural choice: spread on the bread, it coats the crumb, binds the dry meat to the slice, and lays a cooling layer against the chilli all at once, doing the job the marinade's yoghurt did before the tandoor drove it off. The chicken is sliced or pulled so the spiced surface is distributed through the sandwich instead of trapped in one slab, and crisp salad, cucumber, red onion, lettuce, adds a water-cool crunch that breaks the heat further. The bread is kept fairly plain and soft so it carries rather than competes; butter or the raita itself seals it against what little moisture there is. The calibration is the craft: enough cool to make an intensely spiced, dry filling edible in one hand, not so much that the char and the smoke are washed out.
The variations stay inside the spiced-meat-against-cool frame and mostly swap the marinade or the carrier. Chicken tikka uses a similar but differently spiced yoghurt cure for a softer, less charred result. A naan or flatbread folded round the same filling reads as the curry-house wrap rather than a sandwich. Paneer in place of the chicken keeps the tandoor logic meat-free, and a fierier marinade pushes the heat up against the same cooling counter. Each deserves its own article rather than being crowded in here.