Preheat your oven to 375°F (190°C).
Dice the potato into small 1/2-inch cubes and thinly slice the zucchini and onion.
Heat the olive oil in a 10-inch oven-safe non-stick skillet over medium heat.
Add the diced potatoes to the skillet and cook for 8-10 minutes, stirring occasionally, until tender and lightly browned.
Add the onion and zucchini to the skillet and sauté for another 5 minutes until the vegetables have softened.
Stir in the baby spinach and cook for 1 minute until just wilted, then spread the vegetables into an even layer.
In a medium bowl, whisk together the egg whites, whole eggs, sea salt, black pepper, and garlic powder until well combined.
Pour the egg mixture over the vegetables in the skillet, ensuring the liquid reaches all the edges.
Transfer the skillet to the oven and bake for 12-15 minutes, or until the center is set and no longer jiggles.
Remove from the oven and let rest for 5 minutes before slicing into wedges and serving.