Cut guavas in half and scoop pulp from the centers into a one cup measure. In a 1- to 2-quart pan combine sugar and water. Bring to a boil over high heat. Boil until mixture is reduced to about half cup (about 5 minutes). Let cool. In a food processor or blender, Process the guava pulp and lemon juice until pureed. Mix syrup and fruit puree; pour into a 9-inch square metal pan. Cover and freeze until almost firm (about 1 hour). Break frozen puree into small pieces. Process briefly in a food processor just until smooth and slushy; do not over process. Wrap airtight and freeze until firm (at least 2 hours). To serve, let sorbet stand at room temperature to soften slightly, then scoop out. Makes about 3 or 4 servings.
