In a large mixing bowl, stir together the flour, baking soda, baking powder, salt, and ground cinnamon. Set aside.
In a medium bowl, stir together the agave nectar, vegetable oil, milk, lemon juice, and vanilla. Pour the wet ingredients into the dry ingredients and mix together with a rubber spatula until just combined. (Do not over mix.)
Grease a donut pan. Pour the batter into each mold until they're filled.
Bake for 25-30 minutes, or a toothpick inserted in the center comes out clean.
Remove from the oven and let the donuts rest in the pan for 5 minutes. Then, transfer to a wire rack to cool completely.
Cream Cheese Frosting
Beat cream cheese, butter, and vanilla together in a medium mixing bowl with a hand mixer until light and fluffy, about 1 minute.
Add the powdered sugar 1 cup at a time, mixing after each addition until the frosting is smooth and creamy.
Frost each donut and top with sprinkles if desired. Serve immediately.