Preheat the oven to 375°F (190°C).
In a frying pan over medium heat, add a little oil and sauté the chopped onion until translucent, about 3-4 minutes. Add minced garlic and sauté for another minute until fragrant.
Add the fresh spinach to the pan and cook until wilted, about 2-3 minutes. Remove from heat and let it cool slightly.
In a mixing bowl, whisk together the eggs, milk, salt, black pepper, and nutmeg (if using).
Reduce the temperature of the oven to 350°F (175°C) and place the pie crust in the pie dish.
Spread the sautéed spinach mixture evenly over the crust, followed by the shredded cheese.
Pour the egg mixture over the spinach and cheese, ensuring it is evenly distributed.
Bake in the preheated oven for about 30-35 minutes, or until the quiche is set in the center and lightly golden on top.
Let it cool for 5 minutes before slicing and serving.