Combine soy sauce, sugar, and ground pepper in a small bowl. Stir to mix.
Place chicken thighs in a bowl. Pour marinade over chicken thighs. Flip chicken thighs to get them coated with marinade.
Heat vegetable oil in a small skillet. Sauté green pepper for 1 minute. Remove and set aside. Leave remaining oil in the pan.
Pan fry marinated chicken thighs (reserve the marinade) for 2 minutes on each side. Remove and set aside.
Add minced garlic. Sauté for 30 seconds. Add rice. Stir for 1 minute. Pour reserved marinade, water, and salt over the rice. Stir, cover, and bring to a boil. Reduce heat to medium low and let it cook for 5 minutes.
Remove lid. Place sautéed green peppers and pan fried chicken on the rice. Cover and cook for another 5 minutes. Turn off stove and let it sit for 5 minutes.
To serve, transfer to a plate and garnish with sliced green onion.