Light Italian Wedding Soup

Ingredients

• 1 pound ground dark-meat turkey (93 percent lean)
• 2 cloves cloves minced
• 1 large egg lightly beaten
• 1/2 cup plain dried breadcrumbs
• 1/4 cup Parmesan grated , plus more for serving
• Salt and pepper
• 1 tablespoon olive oil
• 1 medium onion halved and thinly sliced
• 2 cans (14.5 oz) reduced-sodium chicken broth
• 2 cans (14.5 oz) diced tomatoes in juice
• 2 heads escarole (2 pounds total), cored, trimmed, and coarsely chopped