Cheesy Stuffed Meatloaf

Name: Cheesy Stuffed Meatloaf
Ingredients: 1 small yellow onion; 1 medium carrot; 2 medium stalks celery; 3 cloves garlic; 1/2 medium bunch fresh parsley; 1 cup dry, plain breadcrumbs; 1 large egg; 1/4 cup whole or 2% milk; 2 teaspoons kosher salt; 1 1/2 teaspoons Worcestershire sauce; 1 teaspoon dried Italian seasoning; 1/2 teaspoon freshly ground black pepper; 1/4 teaspoon red pepper flakes; 1 1/2 pounds 93% lean ground beef; 8 ounces fresh mozzarella or white sharp cheddar cheese (not shredded); 1/3 cup ketchup; 3 tablespoons packed light or dark brown sugar; 1 tablespoon prepared yellow mustard; 1/4 teaspoon kosher salt