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 ½-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