Preheat your oven to 375°F and lightly grease a 9-inch pie dish with a small amount of olive oil.
Heat the olive oil in a medium skillet over medium heat, then add the diced yellow onion and sauté until translucent, about 4 minutes.
Add the fresh baby spinach to the skillet and cook until just wilted, then remove from heat and set aside to cool slightly.
In a large mixing bowl, whisk together the whole eggs, liquid egg whites, sea salt, black pepper, and ground nutmeg until the mixture is frothy and well-combined.
Spread the diced ham, sautéed onions, and wilted spinach evenly across the bottom of the prepared pie dish.
Sprinkle the shredded Swiss cheese over the ham and vegetable layer.
Pour the egg mixture slowly over the fillings, ensuring everything is submerged and the cheese is distributed.
Place the dish in the center of the oven and bake for 25 to 30 minutes, or until the center is set and the top is lightly golden brown.
Allow the quiche to rest for 5 minutes before slicing into wedges to serve.