Place the cantaloupe, mint, orange juice and zest in a food processor and finely puree. Sweeten to taste with honey, if desired. Pour the mixture into a 9 x 13-inch pan (do not use aluminum). Freeze, uncovered, for 45-60 minutes, or until ice begins to form at the edges of pan. Whisk to distribute the frozen portions evenly. Freeze, uncovered, until completely set, at least 3 hours or overnight. Remove from the freezer and with the tines of a sturdy fork, scrape the top of the frozen mixture down the length of pan to form light, icy flakes. Keep scraping until you reach the bottom of the pan. Freeze for 1 or 2 hours more, or until ready to serve. Scoop the granita into ice-cold, fancy glasses; garnish with mint sprigs. Serve immediately.