Preheat the oven to 350°F and oil a baking donut pan with 6 donut cavities.
In a medium-sized mixing bowl, beat the oil, sweetener of your choice, egg yolk, milk, and vanilla extract together until it's combined. Mix by hand with a whisk or with a hand mixer.
In a separate mixing bowl, whisk the flour, baking soda and powder, and salt together until combined. Add it to the wet ingredients and mix until thoroughly combined.
Place the donut batter in a piping bag or zippered bag and cut the corner off. Pipe the batter into the 6 cavities in the donut pan. They shouldn’t be full to allow the batter to rise while baking.
Bake the donuts for 10-12 minutes, or until they are golden brown around the edges and a toothpick inserted in the center comes out clean.
In a small saucepan, combine the tablespoon of light agave or honey and 2 teaspoon of water. Heat it over medium-low heat, stirring occasionally, until they are thoroughly combined in a syrup.
Turn the donuts out onto a cooling rack. Brush both sides with the syrup while still warm. Allow the donuts to cool.