Pizza Dough Chicken Empanadas

Name: Pizza Dough Chicken Empanadas
Ingredients: 3 cloves garlic, crushed; 1 onion, quartered; 1 1/2 teaspoons salt; 1 1/2 pounds bone-in chicken breasts (about 2); 1 bay leaf; 8 tomatillos, husks removed and rinsed; 2 jalapenos, stemmed and halved; 1/2 cup lightly packed fresh cilantro, tender stems and leaves; Salt and black pepper; All-purpose flour, for dusting; 2 pounds purchased pizza dough from your local pizzeria; 1 egg beaten with 1 tablespoon water; 6 ounces shredded mozzarella, optional