1.Preheat the oven to 350°F.
2.Heat 10-inch non-stick skillet on stove and add the oil over medium heat. When it begins to smoke lightly, shut off the heat and add the almonds. Stir them to coat with the oil and put the skillet back on the heat. Cook over low heat, stirring constantly, until the nuts brown, 30 seconds. Add the rosemary and stir until it gets slightly crisp and pale green, 15 to 30 seconds. Use a slotted spoon to remove the nuts and rosemary onto a kitchen towel. Season with a pinch of salt.
3.Whisk together the eggs, water and ½ tsp. salt. Whisk only enough to integrate the eggs. You don't want to whip too much air into them or make them frothy. Place the skillet on the stove over medium heat and add the butter. Swirl the butter around as it melts so it coats the whole surface of the pan. Pour in the egg mixture. Allow mixture to cook for 1 minute then use a wooden spoon to stir the eggs for 1 minute, as if you were scrambling them. Then, allow the eggs to cook, undisturbed, over medium-low heat for about 2 minutes; the eggs will appear to be about halfway set. Sprinkle the cheese and ½ of almond mixture and place the pan in the oven for 5 to 7 minutes or until the center is cooked. Pull out of the oven.
4.Lift the handle of the pan up tilting the pan away from you and towards the plate. This tilting should cause the omelet to slide down in the pan a little. Fold the omelet in half. Sprinkle with the remaining almonds and rosemary. Serve immediately.