Rhubarb Crunch (or Strawberry-Rhubarb Crunch)

This is the only way I've ever really liked rhubarb. I have a tendency to eat it for breakfast, but it's also good a la mode.
The original recipe is made with just rhubarb, but I've found that substituting in as much as half strawberries (and cutting the sugar down by 1/3c per cup of strawberries) is also really yummy.

Makes 9x13 pan

1/3 cups brown sugar
1 cup flour
1 cup softened or melted butter
3 cups rolled oats
Mix together. Press half of the mixture into a 9x13 pan, reserve the other half for the top. (I often do closer to 2/3 in the bottom of the pan, as the under layer gets the juices soaked in and is better than the top in my opinion.)

6 cups finely chopped rhubarb
3 Tbs flour
1 cup white sugar
Mix flour and sugar together. Coat rhubarb by shaking them all together in a covered bowl (or just dump them all into a really big bowl and stir a lot). Put filling in pan on top of under-crust. Cover with remaining crust mixture.
Bake 1 hour at 350.