Heat the oven to 375°F. Cook turkey and onion in oil in a large skillet for 8 to 10 minutes, breaking up the meat, until it reaches 165°F.
Stir in chili powder, cumin, filling salt and garlic powder for 30 seconds. Add beans, tomato sauce, green chiles and broth and simmer for 5 minutes.
Meanwhile, boil orzo in water with the tablespoon salt until 3 minutes short of the package time. Drain thoroughly and fold into the turkey mixture with 2 oz cheddar.
Transfer to a deep 9-by-13-inch baking dish and scatter with remaining cheddar. Cover with foil and bake for 20 minutes.
Uncover for 8 to 10 minutes until bubbling and the center reaches 165°F. Rest for 10 minutes before spooning into bowls.