In a small bowl, lightly mash avocado and half the feta with a fork. Add the lemon juice, parsley, and green onion and stir to combine. Season with salt and pepper, to taste. Add the rest of the feta and stir until just combined. Use immediately. Leftovers will keep covered in the fridge for the rest of the day, but will begin to brown after a few hours. Poach the eggs… bring 4 inches of water and vinegar to a light boil in a medium saucepan, reduce the heat slightly. Make a whirlpool in the water and crack the egg into the whirlpool. Repeat two more times (adding the eggs in different spots in the saucepan. Cook uncovered for 3-4 minutes.Remove with a slotted spoon. To serve… layer watercress, then salmon, avocado mash, and top with an egg. Garnish with extra parsley and chives.