Recipe: Slow Cooker Chicken Parm Meatballs

Name: Recipe: Slow Cooker Chicken Parm Meatballs
Ingredients: 2 (23- to 25-ounce) jars marinara sauce (about 5 cups total), divided; 2 large eggs; 1/2 cup panko breadcrumbs; 1/3 cup finely grated Parmesan cheese, plus more for serving; 1/2 cup minced yellow onion; 1/3 cup coarsely chopped fresh parsley or basil leaves, plus more for serving; 3 cloves garlic, minced; 1 tablespoon kosher salt; 1 teaspoon dried oregano; 1/2 teaspoon freshly ground black pepper; 2 pounds ground chicken, preferably dark meat; 2 cups shredded part-skim mozzarella cheese (optional)