Turn on the broiler. Lay 8 slices of cinnamon swirl bread on a parchment-lined baking sheet. Broil until more than toasted, even a little black in spots.
Flip the slices over, put a square of chocolate on 4 of the slices and a marshmallow on the other four, then broil until the chocolate is melty and the marshmallow is toasty (or burnt—whatever you like).
Sprinkle a flaky salt on the melted chocolate, then top with the marshmallow-toast. Gobble. This s'more can also be made over a fire, of course.