Prepare Fruit Filling

1. Combine rhubarb, strawberries, and lemon juice in a saucepan. Simmer over medium heat for 8-12 minutes until tender.
2. Stir in granulated sugar and cornstarch; let the mixture come to a gentle boil until thickened, about two minutes.

Prepare Crust

1. Preheat the oven to 350°F and prepare a 13×9 inch baking pan.
2. In a large bowl, sift together flour, oats, brown sugar, granulated sugar, baking soda, and salt.
3. Beat in the softened butter until crumbly, reserving 1.5 cups for topping and mixing this remainder with chopped pecans.
4. Press the remaining mixture into the prepared baking pan as the base.

Assemble and Bake

1. Spread the thickened fruit filling over the crust and sprinkle the crumble topping evenly over it.
2. Bake for 30-35 minutes until the top turns golden brown.
3. Allow to cool in the pan before slicing.

Prepare Glaze

1. In a bowl, whisk together powdered sugar, heavy cream, and vanilla extract until smooth.
2. Drizzle the glaze over the cooled bars before serving.