Preheat oven to 375 degrees.
Lightly coat the game hens with olive oil.
Stuff the inside of the game hens with the mirepoix.
Generously season the outside of the game hens.
Roast in the oven for approximately 60 - 75 minutes, until the game hens reach an internal temperature of 165 degrees.
While game hens are in the oven, melt the butter. And add the parmesan cheese and garlic powder; stir to combine.
When the game hens are done, pour on the butter mixture.