Crack egg into a small bowl. Be careful not to split the egg
Fill a saucepan full of water - you want there to be about 3-4 inches of water. Add 1 tablespoon rice vinegar. When the water is almost to a boil and is simmering, add the egg gently into the water bath.
Cook the egg until whites are completely set and yolks begin to thicken but are not hard, 3 to 5 minutes. Do not stir. Lift egg from water with slotted spoon. Drain in the egg on paper towels. At this point, you may want to trim any rough edges, if desired.
Place egg on top of toast. Sprinkle matcha salt (green tea salt) on top of the poached eggs. Serve immediately.