Heat the cooking oil in a large pan or skillet over medium-high heat.

Add the diced chicken and cook, stirring occasionally, until browned and cooked through, about 5-7 minutes. Remove chicken from the pan and set aside.

Add the diced zucchini and bell pepper (and optional onion, if using) to the same pan. Cook, stirring, until vegetables are slightly softened but still have a little bite, about 5-6 minutes.

Add the minced garlic to the pan and cook for another minute until fragrant.

Return the cooked chicken to the pan with the vegetables. Season with salt and pepper, stirring to combine.

Pour the whisked eggs evenly over the chicken and vegetable mixture. Let the eggs set slightly for about 30 seconds.

Gently stir the mixture to scramble the eggs until they are cooked through and no longer liquid.

Stir in the grated cheese until it's melted and gooey.

Serve immediately, optionally garnished with fresh herbs.