Mix boneless and sliced/cubed chicken pieces with chopped garlic, salt, pepper, soya sauce, and mustard paste.
Set aside this marinated chicken in the fridge for 10 minutes at least.
Meanwhile, you can chop bell pepper, onion, tomato and cucumber. In a bowl, mix all these vegetables with a pinch of salt+pepper and 2 tablespoons of vinegar.
In a non-stick pan, pour 1 tablespoon of cooking oil and fry the marinated chicken mixture for 10 minutes or until the meat is cooked well. Tip: You can sprinkle 2 tablespoons of water on the chicken and once the water is dried, your chicken is nearly ready.
Now add the vegetable mixture to the fried chicken in the pan. Cook the entire mixture for at least 10 minutes, stirring now and then. Tip: No need to overcook the vegetables with the chicken.
Cut open your pita bread slices or halve the dinner rolls. Add cheese slices.
Use any serving spoon to scoop in your delicious chicken+vegetable mixture from the pan to the pita slices/dinner rolls.
Add chopped lettuce inside the pita slices or dinner rolls for finished effect.
You're ready to devour these hot shawarmas!
Optional Salsa Dressing: Mix the said measurements of ketchup, vinegar, sugar and salt in a small bowl and serve with hot shawarmas!