Chicken tikka and raita is the tikka sandwich whose defining element is cool rather than sweet, and the raita is doing two jobs that pull against each other. It is the cooling counter, a yoghurt sauce with cucumber and often mint that tempers the charred heat of the spiced meat and stops the filling reading as one hard, dry, savoury note. It is also, by nature, wet, which is the last thing dry bread wants pressed against it. The sandwich is defined by how it gets the cooling benefit of the raita without paying the sogginess that loose yoghurt would normally cost, and that tension is the whole interest of the build.
The craft is thickening and barrier work. Raita for a sandwich is not the pourable bowlside version. It is strained or made stiff, the cucumber salted and squeezed dry first, so it clings to the tikka and cools it without running to the corners and collapsing the bread. The tikka is diced small so the raita can coat each piece, and that coating is the moisture the dry meat was missing, delivered cold and controlled rather than as a spill. The bread is plain and soft so it gives way to firm meat, and it is buttered edge to edge before anything else as a fat barrier between the crumb and the yoghurt, because butter waterproofs where raita would soak. The leaf, when present, goes in dry for a crisp neutral break. Pressed and eaten reasonably soon, the sandwich should taste of char and spice arriving warm-edged and then immediately cut by something cold and clean, which is the entire reason the pairing exists.
The variations are the rest of the tikka family, sorted by what each sets against the spice. Chicken tikka and mango chutney answers with sweetness instead of cool; the plain chicken tikka sandwich relies on a bound dressing and no distinct counter; the chicken tikka wrap rolls the same cooling pairing into flexible bread. Each deserves its own article rather than being crowded in here.