Preheat the oven to 350°F (180°C) and grease a baking dish.
In a large bowl, combine chicken, rice, onion, garlic, and half of the shredded cheese.
Stir in diced tomatoes with green chiles if using, salsa or enchilada sauce, sour cream, and milk or broth.
Season with cumin, salt, and black pepper, then mix until well combined.
Spread the mixture evenly in the prepared baking dish and sprinkle the remaining cheese on top.
Bake for 20 to 25 minutes until the cheese is melted, bubbly, and lightly golden.
Remove from oven, let rest a few minutes, then garnish with green onions, cilantro, or jalapeños.
Serve warm.