Prep the steak by slicing it into thin, bite-sized strips and seasoning with half of the salt, pepper, and garlic powder.
In a small bowl, whisk together the whole eggs and egg whites until well combined and slightly frothy.
Heat avocado oil in a large non-stick skillet over medium-high heat.
Add the sirloin strips to the skillet, searing for 2-3 minutes until browned but still tender; remove steak from the pan and set aside.
In the same skillet, add the diced onions and bell peppers, sautéing for 4-5 minutes until the vegetables are softened and slightly caramelized.
Lower the heat to medium and return the steak to the pan, stirring to combine with the vegetables.
Pour the egg mixture over the steak and peppers, gently folding with a spatula until the eggs are just set and creamy.
Season with the remaining salt, pepper, and garlic powder before serving immediately.