Make the bark: Preheat oven to 350 degrees. Combine the flour, oatmeal, walnuts, sugar and a pinch of salt in a bowl. In a saucepan, over medium heat, melt the butter and cook until light brown, about 6 minutes.
Stir into the dry ingredients. Press the dough into the bottom of a 9inch springform pan. Bake until golden brown, about 30 minutes.
Remove the crust from the oven and sprinkle with the chocolate; let stand until soft, then spread with the back of a spoon. Refrigerate the bark until firm, about 30 minutes. Break into pieces.
Make the oatmeal cream: Fill a large bowl with ice, Microwave 3/4 cup cream until simmering, about 45 seconds. In a blender; puree the oatmeal, sugar, a pinch of salt, vanilla and nutmeg. Transfer to a bowl and place over the ice; in a bowl whisk the remaining 3/4 cup cream until soft peaks form; fold into the oatmeal puree.
Layer the oatmeal cream, bananas and crushed bark in 4 parfait glass. Refrigerate until ready to serve.