Preheat your oven to 350°F (175°C).
In a medium saucepan, combine the rice and broth. Bring the mixture to a boil over medium-high heat.
Once boiling, reduce the heat to low, cover with a lid, and let it simmer for about 15 minutes, or until the rice is tender and the liquid has been absorbed.
While the rice is cooking, in a separate bowl, mix together the melted butter, milk, garlic powder, salt, and black pepper.
Once the rice is cooked, remove it from heat and fluff it with a fork.
Stir in the butter-milk mixture, shredded cheddar cheese, and grated Parmesan until well combined.
Transfer the cheesy rice mixture to an oven-safe baking dish, spreading it out evenly.
Bake in the preheated oven for about 10 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let cool slightly before serving. Garnish with chopped green onions, if desired.