In a medium saucepan, combine 2 ½ cups of water and the oat milk and place over medium heat. Rinse the barley through a fine mesh sieve and add to the saucepan. Grate one apple and add to the saucepan along with the kosher salt and 1 teaspoon cinnamon. Stir to combine.
Bring the porridge up to a simmer then turn the heat to low. Cover and let cook until the barley is tender, about 45 minutes, stirring occasionally. The porridge is done when the barley is tender and creamy. If you want the porridge to be even creamier, you can add a bit more oat milk and cook for a few minutes more. Add 1 tablespoon honey, or more to taste, if you prefer a sweeter porridge.
Quarter and remove the cores from the remaining two apples. Chop into bite sized pieces. Place a non-stick skillet over medium high heat. Add the apples along with the remaining ¼ cup water and ½ teaspoon cinnamon and stir to combine. Cook the apples for 2 to 3 minutes until they begin to soften. Add the remaining tablespoon honey and cook for another minute or two until the apples are tender but still have a bit of bite. Remove from the heat and keep warm.
To serve, divide the porridge into bowls. Top with the sautéed apples, a dollop of yogurt and the toasted hazelnuts. Enjoy!