Place the chopped strawberries in a blender or food processor and blend until completely smooth. Pour the puree through a fine mesh strainer to remove the seeds, pressing with a spoon to extract all the juice. You should have about 1/2 cup of smooth puree.
In a medium bowl, beat the cream cheese with an electric mixer until completely smooth. Add the powdered erythritol, vanilla extract, and lemon juice, then beat until well combined. Add the strawberry puree and mix on low speed until evenly incorporated.
In a separate chilled bowl, whip the cold heavy cream with the electric mixer until stiff peaks form, about 3 minutes.
Gently fold the whipped cream into the strawberry cream cheese mixture in two additions, using a spatula with slow, sweeping motions. Be careful not to deflate the whipped cream.
Divide the mousse among 4 serving glasses or ramekins. Refrigerate for at least 2 hours until set and chilled.
Garnish with fresh strawberry slices before serving.
