Ganache coating on a roulade
You'll definitely want to freeze the cake. Once it's frozen, use a spatula to apply a layer of ganache to the side that will be the bottom of the cake, then return it to the freezer. Once that has set, put the cake, ganache/bottom down on a cooling rack on top of a sheet of parchment paper or acetate. Slowly pour your melted ganache over the cake, guiding it with a spatula if necessary to make sure you get it all covered. You'll want the ganache to be just beginning to cool for a thicker coat. Once it's coated, you can roll it in nuts or whatever you like. You'll have a grid pattern on the bottom (depending on how solid the first ganache froze), and possibly some "feet", but the feet are going to be almost unavoidable.

Any extra ganache will be on the parchment or acetate and can easily be stored until you need it again.