Ka'ak (كعك) in its ring form is the sesame bread itself: an oblong loop, thinner along one edge and wider along the other, its whole surface crusted in sesame seeds and its crumb faintly sweet. Described this way it is bread before it is a sandwich, and the angle is exactly that. The loaf is engineered to be both the wrapper and a flavor in its own right, so when it does take a filling the sesame crust and the gentle sweetness are not neutral backdrop but active partners that the filling has to be chosen against.
The making is where the character is set. An enriched, lightly sweetened dough is shaped into the long ring with its uneven band, given time to prove so the crumb stays tender, then pressed or rolled in sesame until the outside is densely coated, and baked until the seeds toast to a deep nutty brown. Done well and eaten fresh, the ring is soft and elastic with a clean chew and a warm sesame aroma; held too long it dries and hardens and the sesame loses its fragrance, the reason vendors keep the loaves moving and warm them on a hot plate before they sell them. A pocket is opened along the wider belly or the loop is slit to make room, and whatever goes in is tucked or spread there, usually with a brief reheat so the crust crisps again and any cheese loosens. A good ring is pliant, sweet-edged, and nutty with toasted sesame; a stale one is brittle and flavorless and beyond saving by anything put inside it.
It varies entirely by what fills the ring, and each filling reads as its own sandwich rather than a variant of the bread. Za'atar with oil is the canonical treatment, the herb-and-sumac mix painted into the warm pocket; cheese, labneh, hard-boiled egg, halloumi, and akkawi are the other standard savory routes, and a sweet chocolate-spread version plays off the dough's own sweetness. The same ring appears in different sizes from different carts, from a small one-hand snack to a larger shared loaf. Stripped of any filling it is still eaten plain and warm, which is the simplest proof of the design: a sesame-crusted, faintly sweet bread that is worth eating before anything is ever put in it.