Preheat the oven to 400 degrees.
Mix the first 5 in a mixing bowl with your hands.
Grab a golf ball size amount of meat (may be bigger or smaller depending on the size of your slider buns) and form a dip in the meat with your thumb.
Place a piece of mozzarella cheese in the center of the dip and form the meat around the cheese to form a meatball.
Spray a 13 x 9 inch baking dish with cooking spray. Pour tomato sauce to cover the bottom of the dish. Arrange the meatballs in a single layer in the bottom of the dish.
Bake for 20 minutes and allow to cool. Refrigerate until the day you need them. (Alternatively you can cook these completely and use right away. Bake for 30 minutes and toss with tomato sauce when they are finished cooking. Follow directions below for putting the sliders together.)
Place cold meatballs in a crockpot with enough tomato sauce to cover the meatballs. Cook on low for 6-8 hours.
Place a meatball on the bottom of the slider bun and top with a basil leaf. Put the bun top on the meatball and secure with a toothpick.