With more than our fair share of rhubarb there is always a crop ready to be cut and used. When faced with this along with a freezer that was already filled with pockets of frozen rhubarb (and other fruit!), I googled rhubarb cake recipe and found this.
1.5 cups quick cooking rolled Oats (not sure why they need to be quick cooking but rolled is good!)
1 cup of all purpose Flour (I have no idea if this is Self Raising or not, i have used both and think Self Raising works better!)
3 / 4 cup of packed brown Sugar (I use soft brown sugar rather than dark but the latter would work I think!)
3 / 4 cup Butter
1 / 4 cup granulated Sugar
2 tablespoons of all purpose Flour (see comment above!)
1 / 2 teaspoon of Ground Ginger (I have used fresh ginger and it works. I used ground dried ginger last night and don't think that 1/2 teaspoon is enough, try twice this!)
2 cups of Rhubarb (The recipe says frozen unsweetened, I have used fresh, frozen and stewed and all seem to work!)
Preheat oven to 350F (180C). Line 8x8x2-inch baking pan with heavy foil (I didn't realise you could get heavy foil, I use aluminium but guess it is all in the pronunciation?!) extended beyond pan edges (not sure why ?!).
Set aside 1 cup oats mixture. Press remaining on bottom of prepared pan (works well to use the back of a spoon to smooth over!). Bake 25 minutes.
Meanwhile, in medium bowl stir together granulated sugar, 2 tablespoons flour, and ground ginger. Add rhubarb; toss to coat. Spread on hot crust. Sprinkle reserved oats mixture; press lightly.
Bake 30 to 35 minutes, until top is golden and filling is bubbly. Cool on rack.
Lift from pan; cut into bars. Store, covered, in refrigerator up to 2 days (don't quote me but it lasts longer than this if you can resist it. I think 2 weeks has been my record as we forgot about them!).
Borrowed from the following website: http://www.bhg.com/recipe/bars/oaty-rhubarb-streusel-bars/