In a small bowl, pour boiling water over oatmeal & margarine; let stand for 10 minutes.
Preheat oven to 350 F. Grease a 9 x 9″ baking dish.
In a large bowl, beat eggs with sugar until fluffy. Add vanilla & oat mixture, blend well.
Sift together flour, baking powder, salt, nutmeg & cinnamon.
Combine flour mixture to creamed mixture, blending carefully.
Pour into prepared baking pan; bake 35 minutes or until tests done. Cool for 10 minutes. Do not remove from pan.
For Frosting: Combine all ingredients. Spread evenly over cake. Broil until frosting becomes bubbly. WATCH CAREFULLY!
Let cake cool enough for the topping to be absorbed into the cake.