After allowing the meatball sliders to cool completely, make sure to wrap them tightly with plastic wrap or aluminum foil. You can keep them frozen for up to three months by storing them in an airtight container or a zip-top freezer bag. To reheat, you can either thaw them in the fridge overnight or put them in the oven directly from frozen. Just preheat the oven to 350°F and bake the sliders for 10-15 minutes. Make sure they're heated all the way through and the cheese is nice and melted.