Place the ice cream in a bowl and allow to soften slightly at room temperature. Fold in the chopped candies with a rubber spatula. Cover and freeze for 40 minutes to firm up.
Preheat a grill pan over medium-high heat. Grill the bread until golden brown and slightly charred, about 2 minutes per side. Spread each slice with some of the chocolate-hazelnut spread. Scoop 1/3 cup of the ice cream mixture onto 6 of the slices. Top with the remaining slices. Enjoy immediately or store the sandwiches in the freezer for up to 5 hours before serving.