Stir the water and 3/4 cup of sugar in a medium saucepan over high heat just until the sugar dissolves. Whisk in the lemon juice. Pour the lemon mixture into an 8-inch square glass dish. Cover and freeze, stirring occasionally, until the liquid just becomes slushy, about 2 hours. Using a fork, scrape the granita every 30 minutes until it is completely made up of ice crystals. (The granita can be prepared up to 2 days ahead. Cover and keep frozen, and scrape every so often so that the crystals stay loose.)
Whisk the ricotta, remaining sugar, and pinch of salt in a medium bowl to blend. Spoon the granita into dessert bowls. Top with a dollop of the ricotta. Zest the lemon peel over the desserts and serve.