Preheat your oven to 375°F (190°C).
In a 9x13-inch (23x33 cm) baking dish, combine the uncooked rice, warm vegetable broth, chopped cabbage, undrained diced tomatoes, lentils, onion, garlic, Italian seasoning, salt, and pepper. Stir well until everything is mixed.
Cover the dish tightly with aluminum foil. Bake for 50 to 60 minutes, or until the cabbage is tender and the rice is mostly cooked through.
While the casserole bakes, prepare the topping. In a blender, combine the cottage cheese and cornstarch. Blend until completely smooth and creamy.
Carefully remove the foil from the baking dish. Pour the blended cottage cheese mixture over the top and spread it into an even layer.
Sprinkle the shredded mozzarella cheese evenly over the cottage cheese layer.
Return the casserole to the oven, uncovered. Bake for another 20 to 30 minutes, until the topping is bubbly and lightly browned in spots.
Let the casserole rest for 5 to 10 minutes before serving. This allows it to set and makes it easier to slice.