For Dutch oven outdoors, light up ~ 25 coals
Mix together flour, oatmeal, brown sugar, cinnamon and butter.
Press 1/2 crumb mixture into greased 12 inch Dutch oven; reserve additional 1/2 mixture for topping.
Cover crumb crust with sliced rhubarb and strawberries.
For the filling, combine sugar, water, and cornstarch in saucepan; cook over medium to medium high heat stirring constantly until thickened and turning clear.
Remove from heat and stir in vanilla.
Pour topping over rhubarb/strawberries in Dutch oven.
Top evenly with reserve crumb mixture.
Bake for 50-60 minutes, start checking at 30 minutes: Dutch oven 17 coals spread evenly on top, 8 on bottom
Remove and let cool slightly, then serve with whipped topping or vanilla ice cream (then eat the leftovers for breakfast in the morning;)