In a mixing bowl, combine the egg whites, Italian seasoning, garlic powder, salt, and pepper. Whisk vigorously until well blended, about 1-2 minutes.

Preheat a non-stick pan over medium heat and spray it generously with avocado oil cooking spray. Sauté the red bell peppers and green onions for about 2 minutes.

Stir in the grape tomatoes and cook for an additional minute. Off the heat, incorporate the baby spinach and return to heat for about 1 minute.

Reduce the heat to medium-low and pour in the egg white mixture over the sautéed vegetables. Cook undisturbed for about 2 minutes.

Lower the heat to low and sprinkle crumbled feta cheese over the omelette. Cover with a lid and cook for 2-3 minutes.

Gently fold the omelette in half and slide onto a plate for serving.