Self-Frosting Chocolate Zucchini Cake

1/2 c. margarine
1/2 c. oil
1 3/4 c. sugar
2 eggs
1 tsp soda
2 1/2 c. flour
4-6 tbsp. cocoa
1 tsp salt
1 tsp baking powder
1/2 c. sour milk (I just use milk and lemon juice)
1 tsp vanilla
2 c. finely grated zucchini

Topping:
3/4 c. chocolate chips
3/4 c. chopped nuts (optional)
3/4 c. brown sugar

Mix margarine, oil, and sugar well. add eggs. Set aside. Sift together soda, flour, cocoa, salt, baking powder. add dry ingredients alternately with cup sour milk. Add vanilla. Blend well. Add zucchini. Stir. grease and flour 9x13 inch pan. Pour batter into pan. Add topping. Bake at 350 for 40-45 minutes.