1. 1. Prepare Your Ingredients: Start by finely dicing your bell pepper and chopping your fresh spinach. Having all your fillings ready before you begin cooking is key to a smooth process.

2. 2. Whisk the Egg Whites: In a medium bowl, pour the liquid egg whites. Add a pinch of salt, black pepper, and optional garlic powder. Whisk vigorously with a fork or a small whisk until the egg whites are slightly frothy. This incorporates air, which helps make the omelet light and fluffy.

3. 3. Heat the Pan: Place a 8-inch non-stick skillet over medium heat. Add the olive oil or avocado oil and swirl to coat the bottom of the pan evenly. You’ll know the pan is ready when the oil shimmers slightly.

4. 4. Cook the Vegetables: Add the diced bell pepper to the hot pan and saute for 2-3 minutes, until they start to soften slightly. Then, stir in the chopped spinach and cook for another minute, just until it wilts. Spread the vegetables evenly across the pan.

5. 5. Pour in Egg Whites and Cook: Pour the whisked egg whites over the cooked vegetables in the skillet. Let it cook undisturbed for about 2-3 minutes, or until the edges start to set and pull away from the pan, and the top is mostly set but still slightly moist.

6. 6. Add Cheese and Fold: Sprinkle the shredded mozzarella cheese evenly over one half of the omelet. Using a spatula, carefully fold the other half of the omelet over the cheese-filled side.

7. 7. Finish Cooking: Continue to cook for another 1-2 minutes, or until the cheese is melted and gooey, and the omelet is cooked through to your desired doneness.

8. 8. Serve Immediately: Carefully slide the omelet onto a plate. Garnish with fresh chives or parsley if desired, and serve hot.