In a medium non-stick skillet, heat the extra virgin olive oil over medium heat.
Add the diced red onion, red bell pepper, and baby bella mushrooms to the skillet and sauté for 4-5 minutes until the vegetables are tender and fragrant.
Add the baby spinach to the skillet and cook for 1 minute until just wilted.
While the vegetables cook, whisk together the large eggs, liquid egg whites, sea salt, and black pepper in a small bowl until well combined.
Pour the egg mixture over the sautéed vegetables in the skillet, ensuring the liquid covers the entire surface.
Reduce the heat to medium-low and cover the skillet with a lid for 3-4 minutes, or until the eggs are mostly set on top.
Sprinkle the crumbled feta cheese, fresh chives, and fresh parsley over one half of the omelette.
Carefully fold the omelette in half using a spatula and cook for another 30 seconds to melt the cheese slightly.
Slide the omelette onto a plate and serve immediately.