Make the coleslaw: In a large bowl, whisk together the buttermilk, mayonnaise, apple cider vinegar, sugar and remaining half of the scallions from the meatballs, add the cabbage and stir until evenly coated. Season with salt and pepper.
[Here is where, if you’re unhinged enough to make your own barbecue sauce, you can do so using the quickie recipe at the end. But there is truly no need to do this to make a great meatball slider, promise.]
Toast your buns: In a large skillet that you will use to make your meatballs, melt 1 tablespoon of butter over medium-high heat. Place your rolls cut-side down in the pan. Cook until cut surfaces are golden brown, about 1 to 2 minutes. Transfer it to a plate or platter where you will assemble your sliders.
Cook the mashed meatballs: Remove the chicken meatball mixture from the fridge and, with wet hands, roll into desired size and number of meatballs to create a more even shape – this will depend on the size of your rolls. Make sure to roll the meatballs smaller than the bun so they fill out the bun once mashed.
Heat your large skillet over high heat for a minute, then brush with about 2 tablespoons oil. Place your first meatballs in the pan and let them sear for 30 seconds to 1 minute before flattening them with a heavy spatula until they are about 1/2 inch thick. Season the meatballs with an additional pinch of salt and pepper. Cook until crispy and deeply browned on the underside, about 3 to 4 minutes – reduce the heat to medium-high if you want them to cook much faster – then turn and sear on the hob second side, until browned on underside, another 2 to 3 minutes. Transfer the meatballs to the prepared buns and repeat the process with the remaining meat.
End: Top each meatball with barbecue sauce, top with a few slices of cucumber and a small dollop of coleslaw, and eat right away.
Quickie Barbecue Sauce: Combine 1/3 cup ketchup, 3 tablespoons each of molasses and apple cider vinegar, 1 tablespoon Worcestershire sauce, and 1 teaspoon chili powder or smoked paprika powder (or half) in a skillet and bring to a simmer over medium-high heat, stirring. Reduce heat to medium and continue cooking, stirring, for 2 to 3 minutes. Season to taste with salt and freshly ground black pepper. Pour into a bowl to serve; Wipe out the pan and continue to use it to toast the buns and bake the meatballs.