Preheat oven to 350 degrees. To make crumb mixture: In a medium bowl, mix together butter, flour, brown sugar and walnuts. Place on lipped cookie sheet and bake 18–20 minutes, stirring occasionally while baking to avoid burning. Spread half of the crumb mixture into the bottom of a 13-by-9-by-2-inch pan. Set aside the rest.
Set aside the rest. Beat sliced strawberries, egg whites, sugar and lemon juice on high speed for 10 minutes. Set aside. Whip heavy cream, then fold into strawberry mixture.
Pour strawberry mixture over crumbs then sprinkle the rest of the crumbs on top. Cover and freeze until set.