Preheat oven to 350°F. Grease and flour an 8 x 8-inch pan. In a large bowl, combine flour, cocoa, salt and baking soda. Make a well in the center, and pour in the oil, vinegar, water, agave and vanilla. Mix well, then pour into an 8 x 8-inch pan. Bake for 20 minutes, or until a toothpick inserted into the center comes out clean. Dust with powdered sugar and swirl thin chocolate syrup over cake when served or serve with whipped topping! So moist!