In medium saucepan, whisk together 3 cups water, sugar, cocoa, chili powder, cinnamon and salt. Bring to boil over medium. Remove from heat; whisk in chocolate until smooth. Whisk in vanilla. Pour into 9-by-13-inch baking pan; freeze. Using fork, scrape icy edges toward center every 30 minutes until mixture is sorbet consistency, about 2 hours.