Preheat oven to 350°F. Spray a 1-1/2-quart casserole with non-stick vegetable spray.
In a large bowl, combine rice, parsley, green onions, and Parmesan cheese.
In a small bowl, combine eggs and milk; beat until blended. Add to rice mixture; stirring until well combined. Stir in salt and pepper. Pour into prepared casserole. Arrange half the mozzarella cheese over the rice; arrange tomato slices on top and sprinkle with remaining cheese. Cover; place casserole in a pan of boiling water.