Slice carrots in diagonals. Cube onion, separate the petals and keep aside. Chop capsicum into cubes. Chop cabbage roughly. Slice green onion into 2 inch long portions. Set aside.
Take cubed chicken in a bowl. Add in salt and black pepper powder along with little bit of cornstarch. Mix really well and set aside for 10 minutes.
Heat 2 tablespoon oil in a wok add in the marinated chicken and sauté on high heat for 3 to 5 minutes till the chicken is cooked. Remove the chicken to a bowl and set aside.
In the same wok add garlic and saute for 30 seconds. Add in spring onion white part and white onion sauté for 30 seconds. Add in carrot, cabbage, capsicum and toss well. Pour in soy sauce along with a pinch of sugar, salt.
Add water as needed and mix everything. Bring every thing to a boil. Add in sautéed chicken and mix well. Simmer every thing for five minutes.
Mix corn starch with some water to form a slurry. Add this slurry slowly into the chicken and mix well and cook till it gets thickened.
Add in black pepper powder, spring onion greens and give one final stir.
Serve this chicken with some cooked rice.