Preheat your oven to 375°F (190°C). I know it's tempting to skip this, but don't. A hot oven is crucial for crispy phyllo.
Cook the chicken pieces in a large skillet with olive oil over medium-high heat until no longer pink, about 6-7 minutes. Season with salt and pepper. Remove to a plate.
In the same skillet (fewer dishes, you're welcome), add the diced onion and cook until translucent, about 4 minutes. Add garlic and cook for another 30 seconds until fragrant but not burnt – burnt garlic is the ultimate mood killer.
Return the chicken to the pan and add the well-drained spinach. Cook for 2 minutes, stirring to combine everything. Remove from heat and let cool slightly.
In a large bowl, combine the feta, Greek yogurt, heavy cream, eggs, dill, parsley, oregano, nutmeg, and additional salt and pepper. Mix well.
Add the chicken mixture to the yogurt mixture and stir until everything is well combined. Pour this into your baking dish.
Now for the fun part – phyllo! Lay one sheet of phyllo over the filling, brush with melted butter, then repeat with remaining sheets, brushing each one. Don't worry if they tear a bit – it adds "character."
Score the top few layers of phyllo into serving-sized portions using a sharp knife (this makes serving easier later).
Bake for 35-40 minutes until the top is golden brown and the filling is bubbling at the edges. Let it rest for 10 minutes before serving (I know it's hard, but patience pays off).