Preheat the oven to 450°F. Line a 13x9x2-inch baking pan foil; brush the foil with the 1 tablespoon olive oil; set aside.
In a large bowl combine the meatball ingredients. Shape the mixture into 24 1 1/2-inch balls and place them snugly into the prepared pan in rows, making sure the balls are touching. Bake until the meatballs are done (160°F), about 20 minutes.
While the meatballs are in the oven, heat 2 tablespoons of olive oil in a large saucepan over medium-high heat. Add the onion, reduce the heat to medium-low and sauté until soft, about 8 minutes. Add the garlic and sauté 2 minutes.
Add the crushed tomatoes, basil, and pepper. Bring to boiling. Add the meatballs and simmer, covered, for 5 minutes, stirring gently occasionally.
Spoon meatball mixture into buns. Sprinkle each with 1 tablespoon mozzarella.