Mini Meatball Sliders for a Party

Name: Mini Meatball Sliders for a Party
Ingredients: 1/2 pound ground beef; 1/2 pound ground pork; 1 large egg; 1/4 cup panko breadcrumbs; 2 tablespoons store-bought pesto; 1 teaspoon kosher salt; 1/2 teaspoon garlic powder; 1/2 teaspoon onion powder; 1/2 teaspoon freshly ground black pepper; 1/4 cup grated Parmesan; 2 tablespoons olive oil; 24 mini party potato buns(buns are attached to each other); 1 cup marinara sauce; 1/4 cup tornfresh basil; 8 thick slices sharp provolone; 2 tablespoons unsalted butter, melted; 1 teaspoon garlic salt