Chocolate Zucchini Cake~Gluten Free

I made this today along with the Tomato Vegetable Soup for tomorrow's Sunday Lunch. 
Ingredients:
3/4 cup brown rice flour
1/4 cup coconut flour (no substitutes)
3/4 cup sorghum flour (can also use amaranth or other gf flour)
3/4 cup tapioca starch
1 teaspoon baking soda
1 teaspoon guar gum
1/4 teaspoon salt
1/4 cup unsweetened cocoa powder
1 cup canola oil
1 1/2 cups granulated sugar
2 eggs
1 cup shredded zucchini
1 cup sour milk
Topping:
3/4 cup brown sugar
3/4 cup chocolate chips
3/4 cup chopped pecans
Method:
Preheat oven to 350 degrees.  Lightly grease the bottom of a 9"x13" baking pan.  In mixing bowl, whisk together all the dry ingredients.
In another large mixing bowl, beat the oil and sugar together for 1 minute.  Beat the eggs in one at a time.  Mix in the zucchini.  Add all the flour and the sour milk (if you don't have sour milk add 1 tablespoon vinegar to the milk, stir and let sit a bit).  Mix with mixer until well combined.  Pour into baking pan. Let this sit for a couple of minutes as it will thicken a bit. Using the same bowl mix the topping ingredients together and sprinkle evenly over the cake batter.
Bake for 35 minutes at 350 degrees until toothpick inserted in center comes out clean.