Crumble the ground beef into a skillet over medium-high heat. Cook and stir until evenly browned. Drain off grease, and stir in the cream of mushroom soup, tomatoes, and uncooked rice.

Cover, and simmer over low heat, stirring occasionally, until rice is cooked, about 15 minutes.

Preheat the oven's broiler. Transfer the cooked mixture to a casserole dish, and cover with shredded mozzarella cheese.