My gravy for my mash potatoes tastes bland
The recipe says "Salt and pepper to taste" maybe you did not add enough ?

In any cases, the recipe looks really bland; there's not much flavor in there.

You need to build the flavors from the start. 

This is what I would do.


I'd cook the onions first to golden brown and put aside.
I'd cook the meat until brown and crispy (add some salt and pepper)
Add the onions back to the meat. 
(my addition) Add some tomato purée; add some herbs, add some spices; continue cooking until "dry"
Continue with the recipe, adjust seasoning.