Add oats and water to a saucepan and place over medium heat, bringing to a low boil and cooking until almost all of the water is absorbed, stirring occasionally (about 3-5 minutes). The mixture should start to thicken up.
Lower heat to low and add non-dairy milk, cashew butter, vanilla, salt and sweetener of choice.
Add chia seeds, flax seeds and matcha, and stir to combine until smooth. Continue to cook and stir until all the liquid is absorbed and your desired consistency is reached (roughly another 3-5 minutes). If you prefer your oats more runny, feel free to add more non-dairy milk. If you prefer them thicker, cook for a bit longer.
Transfer to a bowl, garnish with toppings of choice and additional sweetener if needed.