- Preheat oven to 400°F and grease a 9×13-inch baking dish with nonstick cooking spray. Press hash in an evenly layer into bottom of prepared baking dish. Bake for 10 minutes.
- Meanwhile, whisk eggs, 1 cup cheddar, spinach, milk, salt, pepper, onion powder and garlic powder together until combined.
- Top hash browns with an even layer of chicken. Pour egg mixture over chicken and top with remaining cheddar. Bake until eggs are set, and chicken is fully heated through, about 35 to 45 minutes.
- Top with chives and serve.
Tip: To make ahead, bake hash according to step 1. Top with egg mixture, and cover and refrigerate overnight. The next day, top with chicken and remaining cheese. Bake according to directions.