Cook the oats: In a small saucepan, bring the water and salt to a gentle boil, stir in the rolled oats, then reduce the heat and simmer, stirring occasionally, until thick and creamy, about 5 minutes.
Rest the oats: Remove the pan from the heat, cover, and let the oats sit for 2 to 3 minutes so they finish absorbing the liquid and become extra creamy.
Cook the egg: While the oats rest, fry the egg in a small skillet with a little oil or butter over medium heat until the whites are set and the yolk is still soft, or cook it to your preferred doneness.
Prepare the toppings: Slice or lightly mash the avocado, finely chop the herbs, and grate the Parmesan so they are ready to add as soon as the oats are hot.
Assemble the bowl: Spoon the hot oatmeal into a serving bowl, stir in the optional olive oil for extra richness, then top with the avocado, cooked egg, Parmesan, and herbs.
Season and serve: Finish with freshly ground black pepper and an extra pinch of salt if needed, then serve immediately while the oats are warm and the egg yolk is still soft.