Corned Beef and Cabbage Slaw Sliders

Serves 6 1/2 cup light mayonnaise 1 tablespoon coarse-grain mustard 1/4 red onion, grated 1 tablespoon cider vinegar Salt and ground black pepper 2 cups finely grated cabbage (about 1/4 head) finely shredded 1 package (16 count dozen small party rolls, split 1 pound thinly sliced deli corned beef Adjust oven rack to lower-middle position...