Preheat the oven to 350 degrees F. Lightly grease a 15-inch by 10-inch baking pan.
Pour the boiling water over the oats and let stand for 10 minutes. Add the margarine and stir until melted. Add the sugars and stir until dissolved. Add the eggs and mix well. Sift together the flour, soda, salt, and cocoa. Add to the oat mixture and mix well. Pour into the baking pan. Sprinkle the chips and nuts, if using, on top.
Bake for 20 to 25 minutes. Cool completely before serving.