For the oat cookies: Preheat the oven to 350 degrees F. Line baking sheets with parchment paper.
In a stand mixer, cream the butter and sugars until fluffy. Add the eggs, one at a time, followed by the vanilla, and mix until just incorporated. Add the flour, salt, cinnamon and baking soda. Mix on low speed until just combined. Add the oats and mix until just combined.
Scoop the dough onto the prepared baking sheets and bake for 8 to 10 minutes. The center of the cookie should be slightly soft. Remove to a cooling rack and let the cookies cool to room temperature.
For the butter cream filling: Fill a pot that is large enough for your mixing bowl to rest on top of halfway with water and bring to a simmer.
Place your mixing bowl over the simmering water and whisk the whites, sugar and vanilla until the mixture is warm and the sugar dissolves.
Place the mixing bowl in your stand mixer and whisk on medium-high until the meringue is cool and thick.
Switch to the paddle attachment and beat in the butter a little at a time until smooth and silky. Fold in the cherries (patted dry if soaked).
To assemble: Pipe 1/2-inch of frosting on half of the cooled cookies and sandwich the remaining cookies on top.