In a stand mixer, stir together flour, baking soda, and salt. Mix in butter, brown sugar, vanilla, and eggs. Add oats and continue to mix.
Chill dough for 1-2 hours.
Shape into 1 and ½ inch balls and arrange on a line baking sheet. Place a pecan half on half of the cookie dough balls (or all.) Bake 10-12 minutes.
To make peanut butter filling, beat together peanut butter, butter, honey, and powdered sugar for three minutes. Assemble sandwiches with two cookies and a spoonful of peanut butter filling.
Recipe by Rachel Schultz at https://rachelschultz.com/2013/07/29/peanut-butter-pecan-oatmeal-cookie-sandwiches/