1. Put the juice, zest, eggs, and sugar in a saucepan.
2. Cook over low flame while stirring constantly with a whisk for about 15-20 minutes, until it thickens. (Make sure to stir constantly or the eggs will curdle.) Remove from flame.
3. Add the margarine and chocolate and mix well until the chocolate melts and the mixture is smooth and uniform.
4. Strain the cream into a bowl and use an immersion blender to achieve a creamy, uniform consistency.
5. Cool to room temperature.
6. Fold mixture into the whipped cream and combine.
7. Pour the mousse into semi-globe silicone molds (or any shape you like) and freeze for six hours before removing from molds.