Preheat the oven to 350 degrees F (175 degrees C). Grease a 9×13 inch baking dish.
Line a rimmed baking sheet with aluminum foil. In a bowl, stir together the flour, brown sugar, walnuts and melted butter. Toast in the oven until walnuts are fragrant, about 15 minutes; stir occasionally. Sprinkle 2/3 of the walnut mixture evenly over the bottom of the 9×13 inch dish.
In a large bowl, whip the egg whites with the lemon juice until they can hold a soft peak. Gradually add white sugar while continuing to whip to firm peaks. Fold in the strawberries.
In a separate bowl, whip the cream with an electric mixer until stiff but not grainy. Fold into the strawberry mixture. Spoon over the crust in the dish and spread evenly. Top with the remaining walnut mixture. Freeze for 6 hours, or overnight.