Preheat the oven to 350F & prepare your baking dish (I like using a bundt pan for the shape, but a 9" square baking pan is what's recommended).
In a small bowl, combine oats and boiling water; let stand until cool (note: this takes a while. You might want to combine the oats and water and brew the coffee, take a break and come back to do the rest to allow time for the liquids to cool).
In a separate bowl, combine flour, baking soda and salt. Set aside.
In a large bowl, cream together margarine and brown sugar until fluffy. Beat in vanilla, oat mixture and flour mixture. Stir in dates & walnuts.
Pour mixture into prepared pan and bake in preheated oven for 30-35 minutes, or until cake tester inserted in middle comes out clean. Set aside to cool.
Prepare the frosting: in a bowl, blend together all frosting ingredients until fluffy. If icing is too thick, add a little more coffee to thin it. If too thin, add icing sugar. Spread icing over cooled cake.