Place the eggs in a small saucepan and cover with cold water by at least an inch.
Bring the water to a rolling boil, then immediately remove from heat, cover with a lid, and let stand for 12 minutes.
Prepare an ice bath in a medium bowl; transfer the cooked eggs to the ice bath for 5 minutes to stop the cooking process.
Peel the eggs and chop them into small, uniform cubes.
In a mixing bowl, combine the nonfat Greek yogurt, Dijon mustard, lemon juice, sea salt, and black pepper, whisking until smooth.
Finely dice the celery and red onion, and mince the fresh dill.
Gently fold the chopped eggs, celery, onion, and dill into the yogurt dressing until thoroughly coated.
Toast the sourdough bread until it is golden brown and sturdy.
Spread the egg salad generously over the toasted sourdough and garnish with an extra pinch of dill if desired.