Whisk the eggs in a bowl until smooth and slightly bubbly. Add soy sauce, salt, pepper, and garlic powder.Stir in cooked chicken, bean sprouts, green onions, carrots, and onion. Dab wet veggies with a paper towel if needed.Heat oil in a nonstick pan over medium heat. Scoop about ½ cup of mixture into the pan and cook 3–4 minutes per side until golden and set.In a small saucepan, combine chicken broth, soy sauce, oyster sauce, and sugar. Add cornstarch slurry and simmer 1–2 minutes until thickened.Serve omelets stacked on a plate and drizzle with warm brown gravy. Garnish with extra green onions or sesame seeds if desired.