Cut top off each tomato. Scoop out pulp, leaving 1/4-inch-thick shells. Chop pulp to measure 1 cup; reserve remaining pulp for another use. Invert tomato shells on paper towels, and let stand 30 minutes.
While tomato shells stand, combine 1 cup chopped tomato pulp, rice, and next 5 ingredients in a medium bowl. Cover and chill 30 minutes.
To serve, spoon rice mixture evenly into tomato shells. Garnish with fresh cilantro, if desired.