Preheat your oven to 400°F (200°C).
In a skillet over medium heat, add the olive oil and sauté the diced yellow onion and minced garlic until fragrant and translucent.
Add the diced chicken breast to the skillet and cook until browned and cooked through, about 5-7 minutes.
Stir in the fresh spinach and cook just until wilted, then remove the skillet from the heat.
In a small bowl, whisk together the Greek yogurt, sea salt, black pepper, nutmeg, and 1 tablespoon of the parmesan cheese.
Fold the yogurt mixture into the chicken and spinach until everything is evenly coated.
Transfer the mixture to a small baking dish and sprinkle the remaining tablespoon of parmesan cheese over the top.
Bake for 10-12 minutes, or until the top is golden and bubbling.