In a medium bowl, combine the sliced strawberries, granulated sugar, and lemon juice. Let them sit for about 15 minutes to macerate.

In a small bowl, sprinkle the gelatin over the cold water and let it sit for about 5 minutes until it blooms.

Heat the gelatin mixture in the microwave for about 10-15 seconds, or until completely dissolved. Set aside to cool slightly.

In a large mixing bowl, whip the heavy cream with the powdered sugar and vanilla extract until soft peaks form.

Puree the macerated strawberries using a blender or food processor until smooth. Stir in the dissolved gelatin until well combined.

Gently fold the strawberry puree into the whipped cream, being careful not to deflate the mixture.

Divide the mousse into serving dishes and refrigerate for at least 2 hours or until set.

Before serving, garnish with additional strawberry slices or whipped cream if desired.