In a bowl, combine the haggis and beans and mix well. Transfer to a baking dish. Spoon the leftover mashed neeps and tatties on top and fluff it up with a fork so that it browns with crispy peaks on top.
Bake in the preheated oven for 30 minutes until bubbling, hot through and browned on top. Remove from the oven and serve.
Haggis alone can be rich, but this pie is very tasty!