Wash the strawberries under cool water and remove the stems.
Cut the strawberries into halves or quarters.
Place the sliced strawberries in a blender or food processor and purée until smooth.
In a bowl, mix the strawberry purée with the granulated sugar and lemon juice until the sugar dissolves.
In a small bowl, sprinkle the unflavored gelatin over the cold water and let it sit for 5 minutes.
Warm the gelatin mixture in the microwave for about 10 seconds until it becomes liquid. Do not let it boil.
Stir the dissolved gelatin into the strawberry purée until well mixed.
Place a mixing bowl and beaters in the freezer for 10 minutes to chill.
In the chilled bowl, whip the heavy cream until stiff peaks form.
Gently fold the strawberry purée into the whipped cream until fully combined.
Divide the mixture evenly into individual serving glasses or bowls.
Chill the mousse in the refrigerator for at least 1 hour to set.
Optional: Garnish with fresh strawberry slices before serving.