Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish.
In a large mixing bowl, whisk together the eggs, whole milk, Dijon mustard, garlic powder, onion powder, salt, and pepper until well combined.
Add the torn croissant pieces to the egg mixture and gently fold in the diced ham and shredded cheddar cheese. Ensure all croissant pieces are well coated.
Pour the mixture into the prepared baking dish, spreading it evenly.
Bake in the preheated oven for 30-35 minutes, or until the casserole is set and the top is golden brown.
Remove from the oven and let it cool for about 5 minutes before serving. Garnish with chopped chives if desired.