In a medium bowl, whisk together the flour, baking soda, cinnamon and salt, then stir in the quick oats. Set aside.
In a large bowl, beat the dairy free butter, brown sugar and granulated sugar for 2 minutes until fluffy. Beat in the molasses, egg and vanilla until smooth.
Add the oat mixture and mix on low speed until combined. Cover and chill the dough for 30 minutes.
Preheat the oven to 350°F and line two baking sheets with parchment paper. Roll the dough into 1 1/2 tablespoon balls, place them 2 inches apart and flatten each one slightly with your palm.
Bake for 9-11 minutes, until the edges are set and the centers are still soft. Cool on the sheet for 5 minutes, then transfer to a wire rack to cool completely.
For the filling, beat the dairy free butter until creamy, then beat in the powdered sugar. Add the marshmallow creme, vanilla and salt and beat for 2 minutes until smooth and fluffy.
Match the cookies up in pairs of similar size. Spread about 2 tablespoons of filling on the flat side of one cookie and top with its partner.Chill for 20 minutes to set the filling, then store airtight, since they get even softer by the next day.