Brush an 8-inch springform tin very lightly with vegetable oil. Line the bottom with a round of waxed paper.
Combine heavy cream and 6 tablespoons confectioners' sugar in the bowl of an electric mixer fitted with a whisk attachment; whip until soft peaks form, about 5 minutes.
Place 8 ounces strawberries in a blender or food processor; puree until smooth. Fold puree into cream. Fold in crushed meringue cookies and raspberry liqueur. Pour into the prepared tin and cover with plastic wrap.
Freeze semifreddo until firm, 6 hours to overnight.
Place 8 ounces strawberries in the blender or food processor; puree until smooth. Press through a fine-mesh strainer to remove seeds. Stir 5 tablespoons confectioners' sugar and lemon juice into the puree until sugar is dissolved.
Spoon strawberry puree onto serving plates. Cut semifreddo into slices and place onto the plates. Garnish with remaining strawberries.