Add oats and water into a high-speed blender and blend for 30 seconds on high.
Place a nut milk bag into a large bowl or the saucepan you will use (or use a piece of muslin cloth over a sieve). Pour the oat milk into the nut milk bag (or muslin cloth).
Gather the edges of the nut bag (or muslin cloth), and squeeze out the milk until only the oat pulp remains. Discard the oats, or you can use the oats in another recipe.
Place the oat milk into a saucepan and heat gently over medium-low heat. Stir continuously with a whisk as it heats. Oat milk will become lumpy as it cooks. If lumps form, whisk continuously to keep it smooth.
Bring the milk to a gentle simmer and continue to stir until it thickens. This should take a few minutes.
Remove from the heat and cool to 110°F. Pour the warm oat milk into a sterile yogurt-making jar. Then add the Prebio Plus, vanilla, salt, and sachet of Yogurt Plus. Mix with a whisk to combine.
Put the lid on the glass yogurt jar and add water to the base of the appliance to distribute the heat evenly. Set the temperature on the yogurt maker to 104° - 110° F. Set the timer to anywhere between 9 and 12 hours. A longer fermentation will produce a tarter-tasting yogurt. If you choose the lower temperature, it should be fermented at the longer time.
When the fermentation is complete, place the yogurt (with the lid) in the fridge for at least 6 hours to cool and set. If you like a less lumpy yogurt, you can use a whisk and stir until more uniform in texture.