Preheat the oven to 350 degrees.
Spray a 13 x 9-inch baking dish with cooking spray, set aside.
Place granola in a food processor, blender or mini chopper. Pulse granola about 5 times. Granola should still be somewhat chunky. Set aside.
Using a serrated knife, slice the rolls in half so you have a slab of top rolls and a slab of bottom rolls. Don't pull the rolls apart, you want to keep them intact. Place the bottoms in the prepared baking dish.
In a large bowl, combine ground duck, ground pork, granola, egg, onion, Parmesan cheese, garlic, parsley, salt, pepper and 1/4 cup marinara sauce. Mix until all ingredients are well blended. (as you would for making a meatloaf) Shape mixture firmly into 1-inch size or golf ball size meatballs; set aside until all the mixture is formed into meatballs. (you will need 24 meatballs. I had a total of 32 meatballs)
Heat oil in large skillet until hot, add meatballs and cook until meatballs are browned on all sides. Brown meatballs in batches and don't over crowd pan. I was able to brown 16 meatballs at once. Remove meatballs to a paper plate to drain excess fat. Continue with remaining meatballs. Cooking times will vary, due to thickness of meatballs and type of ground meat used. Roughly 15 minutes per batch of meatballs.
Spoon off fat in pan, wipe out pan with paper towels to remove all excess fat. Pour remaining sauce into pan and place meatballs back into sauce. Simmer on low, covered for about 1 hour. Remove from heat, cool slightly.
Place meatballs on top of bottom roll, top each meatball with one teaspoon of sauce. Top meatballs with shredded mozzarella cheese or cheese of your choice. Cover with dinner roll top.
For garlic butter:
In a small bowl, combine butter, garlic, basil, and Parmesan cheese, stirring until evenly mixed. Pour garlic butter mixture over top of the sliders. Bake for 15 to 20 minutes or until the rolls are golden brown and cheese is melted. Cut into individual sandwiches. Serve.