Filling:
In a large saucepan, combine rhubarb, sugar, orange zest, and vanilla
Bring to boil over medium-high heat and cook for 4 minutes, stirring frequently
Dissolve cornstarch in water; add to rhubarb mixture
Cook for 1 minute or until thickened, stirring constantly
Set aside
Crumb Mixture:
In a large bowl, mix flour, oats, brown sugar, salt, cinnamon, and pecans
Cut in butter until crumbly
Place about 3 �-cups of crumb mixture in greased 13x9� baking pan
Press lightly to form an even layer
Pour in rhubarb mixture
Spread remaining crumb mixture evenly over the top
Bake at 350* for 30-40 minutes
Cut into bars