Combine rhubarb, strawberries, and lemon juice in a 2-qt saucepan. Cover and cook over medium heat, stirring occasionally, until fruit has thickened to a honey like consistency.
Combine granulated sugar and cornstarch in a small bowl, then mix into the fruit mixture.
Keep cooking, stirring constantly, until mixture comes to a boil (approximately 1 minute). Continue boiling until thickened (1 minute). Remove from heat and set aside.
Combine all crust ingredients in a large mixing bowl. Beat on low speed, scraping bowl often, for 1 to 2 minutes or until mixture is crumbly.
Set aside 1 1/2 cups of crumb mixture.
Press remaining crumb mixture onto bottom of prepared pan. Spread fruit filling over crust, and sprinkle evenly with reserved crumb mixture.
Bake at 350 degrees F for 30 to 35 minutes, or until crust is golden brown.
Cool completely. Mix drizzle ingredients in a small bowl. Drizzle over cooled bars. Cut into bars.
