In a medium pot, bring the chicken broth to a boil, and mix in the wild rice, brown rice, and bay leaves. Reduce heat to low, cover, and simmer 45 minutes, until most of the broth has been absorbed.
In a skillet, melt the butter, and saute onion until tender. Stir in the ground beef, and cook until evenly brown. Mix in the mushrooms, water chestnuts, soy sauce, and curry powder, and continue to cook and stir until heated through.
Preheat oven to 350 degrees F (175 degrees C).
Mix the beef mixture into the rice mixture, and remove the bay leaf. Transfer to a 9x13 inch baking dish. Top with Cheddar cheese.
Bake 20 minutes in the preheated oven, until bubbly and lightly browned.