Preheat oven to 350 degrees F.
Combine rhubarb, strawberries, lemon juice, and orange zest into a medium saucepan.
Cook fruit over medium heat, stirring occasionally until fruit is tender (about 10 minutes).
Stir sugar and chia seeds into fruit mixture.
Continue to cook fruit, stirring frequently for 1-3 minutes until mixture boils.
Continue to boil fruit for 1-2 minutes or until the mixture thickens.
Remove fruit from heat and set aside.
In a large bowl combine flour, oats, oat bran, brown sugar, butter, baking soda, and salt,
Beat crust mixture on low speed until the mixture crumbles.
Grease a 13x9 inch baking pan with butter.
Press crust mixture into the bottom of the baking pan reserving 2 cups for the topping.
Pour fruit mixture over crust carefully spreading fruit close to the edges.
Top with reserved crumble mixture.
Bake for 30 minutes or until browned.
Store in refrigerator.