In a bowl, cream butter & sugars; add egg & rum extract.
In another bowl, combine oatmeal, flour, salt, baking powder, baking soda & cinnamon.
Add flour mixture to butter mixture & combine well. Place cookie dough in refrigerator to chill, (about 30 minutes) while you prepare the filling.
Filling
Peel & chop apples. Chop nuts. Spoon jar of mincemeat into a bowl & combine with apples, nuts & lemon juice.
Assembly & Baking
Preheat oven to 375 F.
Line cookie sheets with parchment paper. Roll chilled cookie dough into generous 1-inch size balls. Place on cookie sheets making sure to give them some room to spread a bit. Press your thumb down in the center making a dent big enough to hold a generous teaspoon of filling. Divide filling between cookies.
Bake for 12 minutes. Remove from oven & allow to rest on cookie sheet for 5 minutes then move to a wire rack to cool completely.