Beat eggs with milk and salt in a small bowl. Heat 1 teaspoon oil in a small nonstick skillet over medium heat. Add the egg mixture and cook until the bottom is set and the center is still a bit runny, 1 to 2 minutes. Flip the omelet over and cook until set, about 30 seconds more. Transfer to a plate. Top with avocado, salmon and basil. Drizzle with the remaining 1/2 teaspoon oil.