Preheat the oven to 350F.
In a bowl or the bowl of a food processor, combine the oats, flour, brown sugar, baking soda and salt. Add the butter and pulse or mix until well blended and crumbly; press half into the bottom of an 8"x8" or 9"x9" pan.
Spread the mincemeat over the base, then scatter the remaining crumbs over top, squeezing them a bit as you go to create larger clumps. Bake for 35-40 minutes, or until golden around the edges. Cool completely before cutting.