Spread half of the chocolate-hazelnut spread on 1 slice of bread, then spread the other half on a second slice. Lay a slice of the remaining bread on top of each to make 2 sandwiches. Cut each sandwich into 6 squares.
In a large bowl, combine the half-and-half, cinnamon and eggs and whisk until fully combined. Add the sandwich squares and toss them around gently in the liquid to fully coat each square.
Divide the sandwich squares between 2 microwave-safe mugs (6 squares in each), then divide the remaining liquid evenly between the mugs. Microwave on high until the bread pudding puffs up slightly and looks firmer, about 4 minutes. Caution, it will be extremely hot.