Prepare a 9” x 5” loaf pan by greasing the bottom and sides. Line with parchment paper a little longer than you’d need and let it hang over the sides for easy removal. Preheat oven to 350° F or 175 C.
Combine the flour, baking powder, baking soda, sugar, and salt in a large bowl. Mix well.
In the center of the ingredients, make a well. Add oat milk, oil, and vanilla. Stir just until well combined.
Add the lemon juice and lemon zest, stirring until completely smooth. As the acid will start reacting with the baking soda, you really need to work quickly. Immediately scrape into the prepared pan and level out the top.
Bake the lemon loaf for about 45-55 minutes. Ovens heat differently, so check it at 45 minutes by inserting a skewer into the center to see if it comes out clean.
The cake should cool for a minimum of 20 minutes before moving it to a cooling rack.
Make the glaze by combining the powdered sugar with just enough lemon juice to make a thick but pourable glaze. It’s best to use a mixing bowl or larger measuring cup with a spout so you can easily pour the icing over the cake.
Once the cake is almost cool, slowly pour the icing over the loaf and allow to set.
This lemon loaf cake is best eaten on the same day as the glaze gets sticky over time. It can be stored in an airtight container in the refrigerator for up to three days. Bring the loaf to room temperature before serving.