Add the Swerve to a food processor and blend until powdered.

Add the mascarpone, lemon juice, 1 teaspoon of lemon zest, and the vanilla to the food processor with the erythritol. Blend to combine until smooth.

Pour the cream into the bowl of a stand mixer. With a whisk attachment, whip the cream until fluffy and doubled in size.

Gently fold the whipped cream into the lemon mascarpone mixture until well combined.

Fold in the remaining lemon zest.

Divide the mousse between 4 serving dishes. Refrigerate for 15 minutes to chill before serving.