Awhile back I joined Kraft Canada's recipe program. They've got great recipes and the thing I really like about them is a lot of them are quick - a real bonus for a single dad. - and I haven't found a clunker in the bunch. April and I had this one last week and it was great. I did make a couple of substitutions and they did nothing to hurt the recipe. Instead of real mashed potatoes I used the packaged ones and I used canned beef gravy. I also threw in a few shots of Worchestershire sauce.
http://www.kraftcanada.com/en/recipes/easy-shepherds-pie-108130.aspx