In a medium bowl, whisk together the large eggs, egg whites, sea salt, black pepper, and garlic powder until the mixture is well combined and slightly frothy.
Heat the extra virgin olive oil in a 10-inch non-stick skillet over medium heat, swirling to coat the bottom of the pan evenly.
Add the diced bell peppers to the skillet and sauté for 3-4 minutes until they begin to soften and develop a light golden char.
Toss in the baby spinach and cook for about 1 minute, stirring constantly until the leaves are just wilted and vibrant green.
Pour the whisked egg mixture over the vegetables, tilting the pan to ensure the eggs reach the edges and cover the filling completely.
Use a heat-resistant spatula to gently lift the edges of the omelette, allowing the uncooked egg to flow underneath until the base is set but the top remains slightly moist.
Sprinkle the shredded mozzarella cheese evenly over one half of the omelette.
Carefully fold the other half of the omelette over the cheese and cook for another 30-60 seconds until the cheese is gooey and fully melted.
Slide the finished omelette onto a plate and serve immediately while hot.