Combine flour, pecans, margarine, and brown sugar together in a bowl until crumbly; transfer to a baking sheet.
Bake in the preheated oven, stirring often, until crumbs are lightly browned, 10 to 15 minutes. Transfer most of the crumbs to a 9x13-inch baking dish.
Beat strawberries, white sugar, egg whites, and lemon juice together in a bowl using an electric mixer on high speed until strawberry filling is smooth, about 15 minutes. Fold whipped topping into strawberry filling; pour over crumbs. Sprinkle remaining crumbs over strawberry filling. Cover dish with plastic wrap and freeze until set, 8 hours to overnight. Cut into squares.