STEP ONEPREPARE Single-Crust Pie Crust according to recipe instructions. Line 9-inch pie plate with crust. Trim and flute edges. Chill until ready to use.
STEP TWOHEAT oven to 425°F. For filling, combine sugar, water, cornstarch and salt in medium saucepan. Whisk until smooth. Stir in blueberries. Cook over high heat, stirring constantly, until mixture comes to a boil. Reduce heat; simmer 2 minutes, stirring constantly. Remove from heat. Stir in mixed berries and lemon juice until evenly coated. Set aside.
STEP THREEFor topping, COMBINE flour, brown sugar, cinnamon and salt in medium bowl. Cut in shortening with pastry blender or fork until mixture is crumbly. Stir in oats.
STEP FOURSPOON filling into prepared pie crust, spreading evenly. Top evenly with crumb topping.
STEP FIVEBAKE on lowest rack 10 minutes. Reduce oven temperature to 350°F. Bake an additional 45 minutes or until crust is golden brown and filling is bubbly. Cool completely on wire rack. Garnish with whipped cream or ice cream.