In a large bowl combine ground beef, onion, garlic, egg, bread crumbs, Italian parsley, cannabis, salt, and pepper. Use clean hands to mix until everything is well combined. Divide mixture into 6 portions and roll each portion into a ball.
Heat oil in a large oven-proof skillet over medium heat. Sauté meatballs for about 5 to 6 minutes, turning frequently until just browned on the outside. Add water to the pan to come up about halfway up the sides of the meatballs. Place pan in oven and let meatballs cook for about 15 minutes or until cooked through. Remove meatballs from oven and increase temperature to 375 degrees F.
To make each sandwich, open roll without cutting all the way through. Spread sauce both side of side of roll. Add meatball and cover with additional sauce. Place a thin slice of mozzarella on top of meatball. Repeat with the remaining sliders. Bake sliders until heated through and cheese is melted, about 7 minutes. Serve immediately.