Preheat oven to 350° F
For the crust & crumble topping: Combine flour, oats, sugar, and salt in a large bowl
Melt butter.
Pour the butter into the dry ingredients and mix until well incorporated and pea-sized crumbles form.
Press half of the mixture into an un-greased 13'' x 9'' pan. Set aside the remaining 1/2 mixture.
For the rhubarb & cream cheese filling:
In a medium bowl, combine cream cheese, sugar, egg and vanilla until very smooth, about 1 minute.
Fold in the chopped rhubarb.
Spread cream cheese/rhubarb filling over the crust.
Then sprinkle the remaining crust crumbles over the top of the filling evenly.
Bake for 45 minutes or until crumble topping is lightly browned.
Let cool completely.
Once cooled, eat right away for the crispiest crumble topping texture.
Store in the refrigerator.