Cut a 1/4-inch slice from stem end of each tomato; discard stem ends. Scoop out pulp, leaving shells intact. Discard pulp and seeds. Invert tomato shells on paper towels to drain.
Combine squash and remaining 9 ingredients; stir well, and spoon evenly into tomato shells. Place shells in a 9-inch square pan. Bake, uncovered, at 350° degrees for 45 minutes or until tomatoes and stuffing are thoroughly heated.