Cook rice according to package directions, omitting salt and fat. Place 2 cups cooked rice in a large bowl; set aside. Refrigerate remaining rice in an airtight container for another use.
Preheat oven to 350°.
Cut tops off tomatoes, and reserve. Carefully scoop out tomato pulp, leaving shells intact; reserve 1/2 cup pulp. Discard remaining pulp.
Heat oil in a medium nonstick skillet over medium-high heat. Add onion; sauté 3 minutes. Add garlic; sauté 1 minute. Add reserved 1/2 cup tomato pulp; cook 5 minutes or until liquid evaporates. Add onion mixture, cheese, and next 5 ingredients (cheese through shrimp) to 2 cups rice.
Place tomato shells in an 8-inch square baking dish. Divide rice mixture evenly among tomato shells; replace tomato tops. Add hot water to baking dish. Bake at 350° for 40 minutes or until tomatoes are tender and rice mixture is thoroughly heated. Serve warm or chilled.