Make the Cookies: Preheat oven to 350 degrees F and place racks in upper-third and lower-third of oven. Line two baking sheets with parchment paper or silicone baking mats; set aside.
In a medium bowl, whisk together the flour, salt, baking powder, baking soda and cinnamon; set aside.
Using an electric mixer, beat the butter, brown sugar, granulated sugar and molasses on high speed until light and fluffy, scraping the sides of the bowl as necessary, about 4 minutes. Add the vanilla; beat until combined. Beat in the eggs, one at a time, scraping down the bowl after each addition.
Reduce the mixer speed to low, add the flour mixture and beat until just combined. With a rubber spatula, stir in the oats. Drop the dough in 2-tablespoonful mounds 2-inches apart onto the prepared baking sheets. Bake until the cookies are set at the edges and slightly soft in the middle, 12 to 14 minutes, rotating the baking sheets halfway through. Let the cookies cool on the baking sheets for 5 minutes, then transfer to wire racks to cool completely.
Make the Filling: Using an electric mixer, beat the cream cheese and powdered sugar on medium-high speed until light and fluffy, about 2 minutes, scraping down the sides of the bowl as needed.
Assemble the Cream Pies: Spread the filling on the flat side of half of the cookies. Sandwich them with the remaining cookies. Store cookies in an airtight container with wax paper or parchment paper between layers, refrigerated for up to 5 days.
Cookie Softness: The cookies will be very soft when you take them out of the oven. That's okay, that's how they're supposed to be, and that's what makes them super-soft to eat even days later.
Cool Completely: I cannot stress to you the importance of allowing the cookies to cool completely. If they are too warm the frosting will melt and you will be left with a melted cream cheese mess.
Filling Amount: I use about 2 tablespoons of frosting per sandwich to get the maximum frosting to cookie ratio.
Storing: Store cookies in an airtight container with wax paper or parchment paper between the layers in the refrigerator for up to 5 days.
Freezing: You can freeze these cream pies by tightly wrapping them individually in plastic wrap and store in the freezer for up to 3 months.