Pre-heat a large wok or deep skillet over medium-high heat. Spray with cooking spray. Sprinkle chicken cubes with salt and pepper then add to pan. Spread chicken in a single layer and cook until browned, stirring occasionally, about 7-9 minutes. Remove chicken from pan and set aside.
While chicken is browning, whisk together chicken broth through sambal in a small bowl; set aside.
To the hot pan where the chicken was browning, stir in onion and garlic and a pinch of salt and pepper. Saute until tender, about 4-5 minutes, stirring frequently. Add green beans and saute until crisp-tender and bright greeen, about 3-4 minutes.
Pour in reserved sauce to pot and use a wooden spoon to scrape up the browned bits from bottom of the pan. Bring heat to high until liquid starts to bubble. Cover pan with lid and reduce to low. Return chicken to pan and simmer for 5 mintues or until green beans are cooked through. Adjust seasoning before serving. Garnish with minced scallions if you wish.