Preheat your oven to 350 deg. Mix oatmeal, brown sugar, flour, salt and butter, and press half of the mixture on the botoom of a 9 x 13-inch baking pan. Spread the rhubarb on top of the crust. Boil the sugar, water, and cornstarch until thick. Add the almond extract, then the pie filling, and spoon the mixture over the rhubarb. Sprinkle the remaining crust ingredients over the top. Sprinkle the nuts over all. Bake for 45 minutes. Serve with whipped cream.