Begin by making the meatballs.
Preheat the oven to 375 degrees F.
In a small saucepan, add the diced onions and oil over medium-low heat. Cook 5 minutes until the onions soften, then transfer to a bowl.
To the same bowl as the onions, add the ground meats, oats, ketchup, milk, egg, Worchestershire, garlic, sugar, vinegar, salt, and pepper. Using a fork or your hands, mix all of the ingredients together until you have one homogenous mixture.
Grease a baking dish for baking the meatballs.
Using an ⅛-cup measuring spoon, scoop and roll your meatballs. Place them into the greased baking dish in one single layer.
Bake for 30-40 minutes until browned on the outside and cooked through.
Once cooked, add your BBQ sauce to a skillet. Turn the heat to medium and add the meatballs. Simmer the meatballs in the BBQ sauce until it becomes sticky, about 3-5 minutes. Remove from the heat.
Meanwhile, make your Mac & Cheese.
Cook and drain your noodles.
To a medium saucepan, add the heavy cream, butter, garlic powder, mustard, and cayenne. Bring to a simmer then reduce the heat to medium-low, allowing the cream to reduce and thicken. After 2-4 minutes and the cream is thickened, cut the heat. Add the cheese and stir gently, allowing the cheese to melt into the cream. Do not boil or simmer the cheese, otherwise, the sauce will break.
Stir in the salt and pepper before tossing the sauce with your cooked noodles.
To assemble, fill a shallow bowl with Mac & Cheese. Top with your BBQ-glazed meatballs. Garnish with fresh chives.