Soak gelatin in 3 tbsp cold water for 5 minutes.
Blend strawberries with sugar and lemon juice until smooth.
Heat the strawberry puree in a saucepan until it begins to simmer.
Stir in the hydrated gelatin until fully dissolved, then transfer and chill in the refrigerator for 15 minutes.
Whip 1 cup of heavy cream with powdered sugar and a few dashes of vanilla until stiff peaks form.
Gently fold the chilled strawberry compote into the whipped cream.
Line dome molds with ladyfingers (optional), then fill halfway with the mousse mixture.
Freeze for 45 minutes to set the mousse base.
Prepare ganache by melting 1 cup chopped semi-sweet chocolate with 1/2 cup heavy cream over low heat. Cool to 90°F (32°C).
Pour the ganache over the mousse layer in each mold, smooth the surface, and return to the freezer for 1 hour to set completely.
Unmold by running a small knife around the edges and place on serving plates.
Dust with a light sprinkle of powdered sugar before serving.