In a small saucepan, combine the gelatin and sugar. Add the water, stir, and cook over medium heat until the gelatin dissolves, about 3 minutes. Remove from the heat and let cool slightly.
In a large bowl, beat the cream cheese until smooth. Add the sour cream, lime juice, tequila, Grand Marnier, lime zest, and salt, and beat to combine. Add the dissolved gelatin mixture and mix well. Pour into the prepared crust and chill until very firm, 3 to 4 hours.
To serve, remove the outer ring from the springform pan. Decorate the center of the cake with the zest strips and the outer edge with a border of lime slices dipped in sugar.
Cut with a thin, sharp knife dipped in hot water and serve.
Yield: about 10 servings