Preheat oven to 375.  Grease a 9x13 inch baking pan.

Crust: In a food processor, pulse the flour, salt, and margarine together until crumbly.  Slowly add in the cold water and mix until the dough starts to form.  You can also do this in an electric mixer.  Press the dough into the bottom of the prepared pan until even.

Filling: In a large bowl, combine the sugar, cornstarch, cinnamon, and vanilla.  Add raspberries and rhubarb and mix until all the fruit is coated.  Spread the fruit on top of the crust in an even layer.

Topping:  Pulse the flour, brown sugar, cold margarine, and salt in a food processor until crumbly.  This can also be done in an electric mixer.  Spread evenly over fruit filling.

Bake 45-60 minutes until the topping is light brown and the filling is bubbly.  Allow to cool completely.

Icing: Stir the powdered sugar, vanilla, and water until smooth and drizzle over cooled pie.  Cut into squares and enjoy!