Heat oil in a deep and wide pan. Add sliced chicken pieces, season with salt and pepper. Cook till chicken is done. Transfer to a plate. In the same cooking pan, add more oil, if required. Add chopped onion and cook till it becomes soft, no need to brown. Add sliced mushroom , season with salt and pepper. Cook till the mushroom is done. Add minced garlic and chopped spring onion, cook for 2 mins. Add cooked chicken to this and mix well.