Preheat the oven to 350°F.
In a large sauté pan over medium heat, brown the sausage in 1 tablespoon of the olive oil.
Remove it to a large bowl.
Sauté the onion, beef, and veal in the remaining 2 tablespoons olive oil until brown and add it to the bowl.
Cook the rice according to the package directions.
In a large bowl, stir together the rice, mozzarella, and Parmesan.
Place the mixture in a casserole dish and bake for 20 minutes, or until the cheese is melted.