Preheat your oven to 375°F (190°C).
Finely dice the chicken breast and the yellow onion.
Heat the olive oil in a non-stick skillet over medium heat, then sauté the onion and chicken until the chicken is cooked through and the onion is translucent.
Add the fresh spinach to the skillet and cook until completely wilted; remove from heat and drain any excess moisture thoroughly to prevent a soggy crust.
In a mixing bowl, combine the cooked chicken and spinach mixture with the crumbled feta, egg, fresh dill, sea salt, black pepper, and nutmeg.
Lightly coat a small oven-safe dish with a tiny bit of oil, then layer the two phyllo sheets into the dish, allowing the edges to hang over.
Spoon the spinach and chicken filling into the center of the phyllo dough.
Fold the overhanging edges of the phyllo back over the filling to create a rustic crust.
Bake for 20-25 minutes, or until the phyllo pastry is crisp and deep golden-brown.
Allow the pie to rest for 5 minutes before slicing and serving.