PREHEAT oven to 325°F. Beat egg whites in large bowl with electric mixer on high speed until soft peaks form. Add salt and baking powder. Gradually add sugar, beating until well blended after each addition; continue beating until stiff peaks form. Add vanilla; mix well. Gently stir in walnuts and crackers. Spread onto bottom and up side of well-greased 9-inch pie plate.
BAKE 25 to 30 min. or until lightly browned. Cool completely on wire rack.
FILL with fruit and whipped topping just before serving.